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I'lnZE ESSAY OF THE ALUMNI ASSOCIATION 
 
 OF THE 
 
 College of Physicians and Surgeons, 
 
 NEW YORK, 1873. 
 ♦ 
 
 ♦♦-.•4 - 
 
 THE EFFECTS 
 
 O F 
 
 High Atmospheric Pressiire. 
 
 IN(M.UI)IN(; THK 
 
 CA J SSCm DISEA SP]. 
 
 Hv ANDREW H. SMITH, M. 1).. 
 
 >#SlTR<}EON TO THK NKW YOKK BRIDCK (.'oMI'ANV, 
 
 Mkmbkk ok the Acadkmy ok Natural Sciknoks, Phji.ai>ki.i"hia ; 
 
 C'ORHKSPONDINtJ MK.MBKR OK THK (iESKLLSCHAFT FUR HEII.K i:NJ)E. 
 
 Berlin; late ok the Medical jStakk of the Re(;ui ak 
 Armv; Sur(;eon to the Throat Department of the 
 Manha'itan Eve and Ear Hospital; Physician 
 to St. Luke's Hosfital, etc. 
 
 lUiOOKLYN : 
 
PRIZE ESSAY OF THE ALUMM ASSOCIATION 
 
 OF THE 
 
 College of Physicians and Surgeons, 
 
 NEW YORK, 1873. 
 
 THE EFFECTS 
 
 OP 
 
 High atmospheric Pressure, 
 
 INCLUDING THE 
 
 CAISSOISr DISEASE. 
 
 Br ANDREW H. SMITH, M. D, 
 
 SURGKON TO THE NEW YORK BRIDGE COMPANY, 
 # 
 
 Member of the Academy ok Natural Sciences, Philadelphia; 
 
 CORRESPONDING MEMBER OF THE GESELLSCHAFT FUR HEILKUNDE, 
 
 Berlin; late of the Medical Staff of the Regular 
 Army ; Surgeon to the Throat Department of the 
 Manhattan Eye and Ear Hospital ; Physician 
 TO St. Luke's Hospital, etc. 
 
 BROOKLYN: 
 EAGLE PRINT, 34, 36 and 38 FULTOX STREET. 
 
 1873. 
 
'1 
 
 • 
 
EEPORT 
 
 ON 
 
 THE EFFECTS OF HIGH ATMOSPHERIC PRESSORE, 
 
 INCLUDING THE 
 
 C^ISSO]Sr DISEASE. 
 
 By ANDREW II SMITH, M. D., 
 
 Surgeon to the Company. 
 
 To the Board of Directors of the Neto York Bridge Company : 
 Gentlemen : — 
 
 This Report was originally inteuded simply to present my own ex- 
 perience as Surgeon to the New York Bridge Company during the 
 sinking of the second caisson. But in endeavoring to compare this 
 experience with that of others who had had opportunities of observ- 
 ing the effects of high atmospheric pressure, I found tliat the litera- 
 ture of the subject consisted only of isolated reports by different 
 individuals, in different languages, and having little or no reference 
 one to another, so that a great deal of research was required to obtain 
 a connected view of the subject. It seemed to me, therefore, de- 
 sirable not to add another to the list of disjointed fragments, but 
 rather to incorporate my own observations with the existing mate- 
 rial, and thus^resent in one view a resume of our actual knowledge 
 upon the subject. This I have endeavored to do briefly in the follow- 
 ing pages. For whatever is purely theoretical, however, and espe- 
 cially as regards the pathology of the Caisson Disease, I must accept 
 the entu'e responsibility, unless reference is made to other authority. 
 
 CHAPTER FIRST. 
 
 HISTORY. 
 
 The discoveries of Torricelli, in 1643, which led to his invention of 
 the barometer, and the further elucidation by Pascal of the principles 
 of atmospheric pressm-e, five years later, were followed by confused 
 and contradictory speculations on every hand as to what would be 
 the effect upon animal life if the barometric changes so eagerly 
 observed assumed a wider range. 
 
 Dr. Henshaw, an English physician, published an essay in 1664, in 
 which he proposed to treat diseases by varying the pressure of the 
 atmosphere by w^hich the patient was surrounded. His idea was to 
 have a room (domicilium) constructed of masonry, and made air- 
 
4 
 
 tight, in which the sick person could remain in an atmosphere which 
 was to be either rarefied or condensed by the action of an organ 
 bellows. 
 
 He fancied that acute diseases would be benefited by an increased 
 pressure, while chronic diseases on the other hand demanded a rare- 
 fied atmosphere. His views seem, however, to have been purely theo- 
 retical, as there is no record of any serious attempt to reduce them to 
 practice. 
 
 More than a century elapsed before the subject again awakened the 
 attention of scientific men. In the year 1783 the Academy of Sci- 
 ences of Haarlem offered a prize for a description of the best appara- 
 tus for experimenting upon the effects of compressed air, with a 
 record of experiments made by means of it on animal life, the growth 
 of plants, and the inflammability of the different gases. This 
 prize, however, was not contended for until more than half a century 
 later. 
 
 Diving-bells were brought into use as early as the beginning of the 
 sixteenth centmy, but the condensation of the air within them does 
 not seem to have attracted attention, at least as affecting the occu- 
 pant. Indeed, whatever influence the increased pressure may have 
 exerted was masked by the j.mpurity of the air, which, in the ma- 
 chines first employed, was not renewed. It was found that the 
 strongest man could not remain under water longer than an hour ; but 
 the ill effects experienced were attributed to the heat which accumu- 
 lated in the bell, and which was supposed to affect respiration. Sub- 
 sequently, when an apparatus was added for supplying fresh air, it 
 was remarked that the workmen felt no inconvenience whatever. 
 
 The first observations of real value upon the effects of high at- 
 mospheric pressm-e were made at Howth, near Dublin, in the year 1820, 
 by a distinguished Russian physician named Hamel. In the course of 
 some engineering work in which diving-bells were employed, Dr. 
 Hamel had the opportunity of studying the effects of compressed air, 
 not only upon the workmen, but also upon himself. In describing his 
 own experience, he states that at the depth of five or six feet severe 
 pain was felt in the ears, which was relieved in a measure by swal- 
 lowing. At fifteen or sixteen feet, there was a noise in the ears like 
 an explosion, followed by entire relief from the pain. His respiration 
 was perfectly easy. 
 
 The ascent was accomplished with much less inconvenience than 
 the descent. 
 
 Hamel states that one of the workmen became so accustomed to 
 the air of the bell as to be uncomfortable under the usual atmospheric 
 pressure.* 
 
 * Bibliotheque ile Geneve, 1820. 
 
5 
 
 In 1826, Dr. Colladon published observations made at the same 
 time and place as the above. In winter the hours of work in the 
 bells were five daily ; in summer, five and ten alternatel}^ Toward 
 the close of the work, each day the men became very much exhausted, 
 and were given a little brandy and a bit of bread. Those newly em- 
 ployed suffered with pain in the head and ears, and were often 
 affected with colic and diarrhoea, wiiich last were attributed to cold 
 and wet. Increase of appetite and augmentation of the urine were 
 observed. In some cases, deafness was relieved, and one case of 
 asthma was entirely cured. 
 
 In 1835, Junod published the results of extensive experiments upon 
 compressed air as a remedial agent. * This was the beginning of a 
 series of memoirs upon this subject appearing in rapid succession in 
 France and Germany. Institutions sprang up in various parts of the 
 Continent designed to afford the most approved facilities for this 
 mode of treatment, and the results obtained w^re, and continue to 
 be, highly satisfactory. The "compressed air-baths" are especially 
 useful in the treatment of pulmonary diseases and of dyspepsia. 
 
 But as the pressure employed in these baths is comparativel}^ slight, 
 usually not more than eight or ten pounds to the square inch, the 
 effects observed differ widely from those produced by the high pres- 
 sure employed for engineering purposes. This difference is not only 
 in degree, but also in kind, and therefore the literature relating to 
 compressed ah* as a remedy,t although rich, and in itself very in- 
 teresting, throws but little light upon the subject of this discussion. 
 It is probable, however, that the investigations in this direction of 
 Junot, Tabai^e, and Pravaz first suggested the employment of com- 
 pressed air as a substitute for pumps in mining operations. 
 
 To M. Triger, a French engineer, belongs the credit of first con- 
 ceiving and carrying out a plan by wiiich atmospheric pressure was 
 made to keep back the water flowing into a mining shaft. It had 
 long been known that the valley of the Loire was underlaid by an ex- 
 tensive bed of coal, but, inasmuch as in order to reach the coal it 
 was necessary to pass through twenty metres of quicksand in commu- 
 nication with the water of the river, the engineering difficulties had 
 been considered, until the advent of Triger, as insurmountable. To 
 keep a shaft dry by pumping w^as equivalent to pumping out the 
 Loire. . To meet this difficulty, Triger conceived the idea of sinking 
 an iron tube through the quicksand, the interior of the tube being 
 kept free from water during the excavation b}-- condensing the air in 
 
 * Archives Generales de Medicine. 
 
 t Those interested in this subject will find it exhaustively treated in an admira- 
 ble work by Dr. Rudolf v. Vivenot : " Zur Erkenntniss der Physiologischen Wir- 
 kung und der Therapeutischen Anwendung der Verdichteten Luft." Erlangen, 
 May, 1ST2. 
 
(> 
 
 the tube to the point of counterbalancing the pressure of the water. 
 After some preliminary experiments made by the aid of Tabarie's 
 remedial bath, the work was begun in 1839, near Chalonnes, A tube 
 of iron, seventy feet long by three and one-half feet in diameter, was 
 provided, with a box or chamber at the top, such as we now call an 
 air lock, having a valve above opening inward, and another below 
 opening downw^ard into the tube. These valves were of such a size 
 as to permit the passage of the workmen, and the removal of the ex- 
 cavated material. The workmen having passed into the lock, the 
 upper valve was closed, and a cock opened communicating with the 
 main tube, where the air was compressed sufficiently to keep back 
 the water, the compression being effected by means of condensers 
 worked by steam. The pressure in the lock having become equal to 
 that in the main tube, the lower valve Avas opened and the workmen 
 descended into the tube. In going out, or in sending out material, the 
 process was reversed. The tube was forced down into the earth in 
 proportion as the wwkmen excavated at the bottom. 
 
 It will thus be seen that the first attempt at this mode of working 
 embraced all the essential features of the method as now employed. 
 
 In his undertaking, Triger w^as completely successful. The quick- 
 sand was passed and the coal reached, and at the same time there was 
 given to the world a new engineering resource of exceeding value. 
 
 It is much to be regretted that these operations were not carried on 
 under the eye of a competent medical observer. The onl}^ report we 
 have of them is by M. Triger himself,* and it is natural that the en- 
 gineering rather than the medical aspect of the question should prin- 
 cipally engage his attention. His notice of the effects of the com- 
 pressed air upon the workmen is extremely meagre, and is summed 
 up in the following points : 
 
 "1. At the pressure of three atmospheres it is impossible to whis- 
 tle, Avhile a lower pressure does not produce this effect. 
 
 "2. In the compressed air, every one speaks through the nose, and 
 this is the more noticeable the higher the pressure. 
 
 " 3. All the laborers remarked that in ascending the ladders they 
 were much less out of breath {moins essouffles) than when mounting 
 to a similar height in the open air. 
 
 " 4. A laborer who had been deaf since the seige of Antwerp, 
 (1832,) always heard mere distinctly in the compressed air than any 
 of his comrades. 
 
 "No illness was occasioned among the laborers except that two of 
 them, after seven hours of labor in the tube, experienced severe pains 
 
 * Comptes Renclues. T. XIII. 1S41. "Memoire sur nn appareil d air com- 
 prine pour le ijercement des pnits, etc. Par M. Triger. 
 
i 
 
 ill the arms and knees, coming on about half an hour after ascending 
 into the open air." These are the first recorded cases of what I have 
 named the Caisson Disease. 
 
 About the year 1850 compressed air was first employed in the 
 sinking of piers. A railway bridge was constructed over the Medway, 
 between Rochester and Chatham, the piers of which rested on a basis 
 composed of hollow iron piles, fortj'-two inches in diameter, each of 
 which was sunk in precisely the same manner as the tube of Triger. 
 I have not been able to find any record of the effects of the com- 
 pressed air upon the men employed, though some accidents due to 
 this cause are stated to have occurred. 
 
 The results obtained by Triger led, in 1845, to the application of 
 the same principle to the working of the mine at Douchy, Depart- 
 ment du Nord. The laborers in this case were under the supervision 
 of MM. B. Pol and T. J. J. Watelle, who published an extremel}^ in- 
 teresting memoir upon the subject.* 
 
 The entire personnel comprised sixt3'-four men, who were employed 
 at two different epochs, under different pressures. They were 
 divided into gangs of six or seven each, laboring alternately four 
 hours twice a day. At first, the time allowed for locking out wa^s 
 one-fourth of an hour, but as the pressure increased it wa^s extended 
 to half an hour. The maximum pressure was three and one-half 
 atmospheres. 
 
 After each shift the men bathed and put on dry clothes, when a 
 cup of bouillon and a glass of Bordeaux were served to each man. 
 
 As the number of cases of illness increased, a sort of amhulance, or 
 temporary hQ#pital, was established at the spot. 
 
 At a pressure of two and three-quarter atmospheres, Pol experi- 
 enced in his own person the pain in the ears while lockmg in, and the 
 ease with wliicli a ladder is ascended in the compressed air, confirm- 
 ing in this latter pai'ticular the observation of Triger. The soot from 
 the candles with which the an* of the shaft was loaded, produced a 
 troublesome cough, attended with black expectoration. The mucous 
 membrane of the nose and throat became stained with it, and even 
 the faeces were blackened. 
 
 While locking out there was experienced by all the men a feeling 
 of suffocation. Pol was the first to perceive that the real danger was 
 in passing from the condensed into the normal atmosphere, instead of 
 in passing in the reverse direction. On emerging into the open air, 
 he found that his pulse, which had fallen while in the caisson from 
 seventy, its normal standard, to fifty -five, rose suddenly to eighty- 
 five. When the pressure had increased to three and one-half at- 
 
 * Memoire sur les EfTets de la Compression de Pair, etc. Annales d' Hygiene 
 Publique et de Med . Legale, 1854. 
 
8 
 
 mospheres, he again entered the caisson. The unpleasant sensations 
 already referred to were found to be intensified. In blowing his nose 
 he accidentally discovered that this operation gave much more perfect 
 relief to the ears than the act of SAvalloM'ing. In speaking he found 
 that the tongue moved stiffly and with difficulty. Sounds were not 
 heard with, their usual intensity. The secretion of urine Avas decid- 
 edly increased. After reaching home he was seized with severe pain 
 in one arm and shoulder, and in the walls of the chest. Afterward, 
 there were chills, followed by vomiting. Rest in the horizontal po- 
 sition, and the use of sudorifics, restored him to his usual health by 
 the following day. 
 
 Of the sixty-four men employed, thirty-nine continued until the 
 work was completed, and twenty-five were compelled to give up their 
 places, not being able to support the effects of the compressed air. 
 
 The most usual affection was muscular pains, occurring either alone 
 or ushering in other symptoms. Pulmonary congestion occurred in 
 several cases, but it may well be questioned whether the excessive 
 impurity of the air, as evinced by the amount of soot it contained, 
 may not have had much to do with the production of this otherwise 
 unusual result. Other s;>^nptoms which he describes, such as great 
 hebitude, incoherence of speech, tottering gait, etc., indicate the 
 effects of carbonic acid, and as no mention is made of any provision 
 for removing the products of combustion and respiration, this gas 
 must have been present in considerable quantity. 
 
 The conclusions arrived at by Pol are as follows : 
 
 1. A pressure of four and one-quarter atmospheres is not in itself 
 dangerous, but the return into the open air may cause serious acci- 
 dents, and even sudden death. The danger is in proportion to the 
 previous pressure. 
 
 2. The pathological changes consist in visceral congestions, among 
 which congestion of the lungs and brain take the foremost rank. 
 
 3. The tendency to these congestions increases with the age, at 
 least between eighteen and fifty-five. 
 
 4. Not the period of greatest strength, which is between thirty and 
 forty, but that betAveen eighteen and twenty-six is that which is ex- 
 posed to the least danger. 
 
 5. Experience teaches that the ill effects are in proportion to the 
 rapidity ^^dth Avhich the transition is made from the compressed air to 
 the normal atmosphere. 
 
 6. Unimportant troubles, such as cough, gastric symptoms, etc., 
 may be due to the smoke from the lamps. 
 
 7. The treatment is not different from that which is usual wh( n 
 like symptoms arise from other causes. The first indication is to 
 
9 
 
 bring about a reaction, wliich is iu turn to be conibatted Avhcn it ex- 
 ceeds physiological limits. 
 
 8. One case seems to indicate that the quickest and safest means of 
 restoration is an immediate return into the compressed ah. 
 
 9. Cold to the surface is the best means for restoring the function of 
 the skin. 
 
 About the year 1856 this metliod of excavation was employed in 
 the coal mines at Eischweiler, near Aix-le-Chapelle. Xo phenomena 
 were observed differing from those already described, except that 
 bleeding from the nose occurred in several cases on emerging into 
 the open au\* 
 
 About 18o8-9 excavation by the aid of compressed air was exten- 
 sively employed in laying the foundations of piers for bridges. 
 Among the first of these were the Quarantine Bridge at Lyons, the 
 bridge at Macon, and the chain bridge over the Thiess. A report 
 upon the latter is contained in the Aunales des Fonts et des Chaus- 
 ses," for 1859. Ringing and pain in the ears were complained of by 
 the laborers, as also pain in the teeth, and in the muscles generally. 
 The sound of the voice was observed to be changed, and the breath- 
 ing to be quickened. The return to the open ah* was often followed 
 by bleeding at the nose. Men of several different nationalities were 
 employed, and it was observed that the Hungarians and the French 
 suffered least, while the Italians. Germans, and Sclavouians were 
 most affected. 
 
 In 1859. the mines at Eischweiler were re-opened, compressed air 
 being again Anplo3Td. The pressure did not exceed two and one- 
 half atmospheres. The dm-ation of the sliifts was six hours. Exces- 
 sive s^veating was observed, followed by thirst after leaving the mine. 
 There was generally impairment of appetite. + 
 
 At the same time work was being carried on by similar means in 
 the coal mines at Liittich. According to the statement of the super- 
 intendent, the men became so emaciated that after a few months they 
 could no longer be prevailed upon to continue the work, notT\ith- 
 standing large wages were offered and the most nourishing food 
 provided. 
 
 Perhaps the most extensive work undertaken in Europe by the aid 
 of compressed air was the bridge over the Rhine, at Strasburg. An 
 accomit of this is given by Dr. Francois, who had medical charge of 
 the workmen. J 
 
 * Vivenot. Wirkimg der Verdichteten Luft. 
 t Ibid. 
 
 t •* Des effets sur les ouvriers travaillant dans les caissons servants de base anx 
 piles du Pont du Grand Khin." Annales d' Hygiene Publique et de Med. Legale. 
 T. XIV. 1860. 
 
10 
 
 The caissons were fourteen in number, eacli seven metres long by 
 five and eight-tenths wide and three and five-tenths high. The 
 locks were two metres in diameter and four metres in height. 
 
 Francois refers to the progressive impairment of hearing as the 
 pressure increased in the lock ; to the increase of temperature from 
 the compK'Ssion of the ah- ; and to the accumulation of soot in the 
 air-passages, Avhich had been before observed by other writers. On 
 going out of the caissons, intense pain in the ears sometimes occurred, 
 together Avith muscular and arthritic pains. A very annoying itching 
 of the skin was sometimes felt. Cerebral congestions, hcemoptysis, 
 and bleeding at the nose, were also not uncommon. Sometimes these 
 various affections occm-red immediately upon leaving the caisson, 
 while in other cases they were deferred for several hours. In two or 
 three instances the men were able to walk home, and afterward fell 
 " as if struck by lightning." The attacks usually passed off quickly. 
 Only one death occurred, and that resulted from breaking the rule as 
 to the length of time to be occupied in locking out. 
 
 The rule established was to allow from four to five minutes in 
 locking out when the pressure was one-quarter to one-half an at- 
 mosphere ; six to seven minutes for one atmosphere ; ten for one and 
 one-half atmospheres ; twel¥e for two atmospheres. A woolen vest 
 was provided for each man to be put on when leaving the caisson, in 
 order to guard against the effect of the sudden reduction of tempera- 
 ture which resulted from the expansion of the air in the lock. It was 
 observed that the foremen suffered much less than the laborers, since 
 their superior intelligence enabled them to realize the necessity of 
 observing the rules. 
 
 Some other points observed by this writer will be referred to here- 
 after in their proper connection. 
 
 In the year 1863, Dr. Antoine Ed. Foley published a monograph 
 comprising his observations upon the effects of condensed air as 
 demonstrated dm-ing the sinking of the piers for a bridge at Argen- 
 teuil.* The original work not being accessible, I avail myself of the 
 resume contained in the treatise of Vivenot, of which I give a some- 
 what condensed translation from the German. 
 
 Foley observes that during the time that the pressure was increas- 
 ing, the organs of hearing were alwaj's, without exception, afifccted. 
 Occasionally neuralgic pains were felt darting through the forehead, 
 the nasal cavities, and the jaws ; the voice acquired a metallic 
 sound ; whistling became impossible ; in a few cases stammering was 
 induced. Taste, smell, and the sense of touch lost their acuteness. 
 There was experienced a sense of warmth in the skin, as if one were 
 
 *"Du travail dans s'air comprime, etude medicale, hygienique et biologique 
 faite au pont d'Argenteuil." Paris, 1863. 
 
11 
 
 in a dryiug-room. The pulse became small and thready, sometimes 
 imperceptible to the touch. The venous blood had a bright red hue. 
 
 The lungs seemed to increase in development, while the motion of 
 the ribs was less. Shortness of breath was not often observed. In- 
 crease of appetite was soon experienced, but never thirst. 
 
 While the pressure remained stationary, all subjective phenomena 
 disappeared, to return again during the locking out. Ringing of the 
 ears and bulging of the ear drums were observed ; taste and smell re- 
 turned ; a prickling sense of warmth was felt in the nostrils, which 
 was sometimes followed by bleeding at the nose. At the same time 
 the rapid decline of the temperature from the expansion of the air 
 caused extreme chilliness. 
 
 At first the laborers remained in the compressed air four hours at a 
 time, twice a day, with an interval of rest. But as the pressure in- 
 creased it was found necessary to diminish the hours of labor. 
 
 The ill effects upon the workmen were almost entirely confined to 
 a distressing itching of the skin and painful congestive swelling of 
 the muscles. They observed that the appetite was increased while 
 thirst was diminished. The flow of urine was also greater than 
 usual. 
 
 A remarkable case is mentioned, in which a man, far advanced in 
 consumption, with an enormous cavity in one lung, and suffering 
 from hectic, persisted in working in the caisson, contrary to the 
 advice of Foley, and at the end of two months had gained ver}^ 
 much in flesh, was looking well, and feeling in the best of health. 
 
 I shall hav^ occasion hereafter, when treating of the Caisson Dis- 
 ease, to refer more in detail to some of the experiences of this writer. 
 
 In the year 1868 there was begun at St. Louis a work which 
 involved the application of compressed air on a scale far exceeding 
 anything before attempted. This was the sinking of two piers and 
 two abutments for a bridge across the Mississippi. The magnitude 
 of the work consisted in the great depth to which it was necessary to 
 sink the caissons, in order to obtain a solid foundation. One of them, 
 at the moment when it touched the rock, was 110 feet below the 
 surface of the water. This implied a pressure within the caisson of 
 50 lbs. to the square inch. The dimensions of the caissons, too, far 
 exceeded those of any before constructed, the average superficial 
 area being about 3,700 square feet. 
 
 A large number of workmen were employed, and an opportunity 
 was presented for studying the effects of compressed air upon the 
 human body on a scale which dwarfed all former experien ces into 
 comparative insignificance. 
 
 The physician in charge was Dr A. Jaminet, whose report is 
 extremely interesting.* It describes a number of valuable experi- 
 
 * Physical Effects of Compressed Air, St. Louis, 1871, 
 
12 
 
 ments upon the boiling point of water at various pressures, electri- 
 cal phenomena, etc., and proceeds to detail the physiological action 
 of high atmospheric pressure as demonstrated upon himself and 
 others. The writer then gives his own experience in an attack of 
 paralysis resulting from a prolonged sojourn in the caisson— a paraly- 
 sis from which he fortunately recovered by the following day. 
 • He next discusses the mode in which the pressure acts to bring 
 about the morbid phenomena observed, and arrives at the conclusion, 
 which the facts do not seem to me to warrant, that the ill effects 
 are simply the result of exhaustion from too rapid tissue-change, 
 caused by the absorption of an excess of oxygen. Following out 
 this idea, he lays down a plan of treatment which consists simply of 
 rest in a recumbent position, with the feet elevated, and the adminis- 
 tration of stimulants and nourishment. 
 
 He describes, more or less in detail, seventy-seven cases, in eight of 
 which death took place. The post-mortem appearances in these are 
 described. They were all characterized by congestion of the brain 
 and cord, and of most of the abdominal viscera. 
 
 Dr. Jaminet's observations are exceedingly valuable ; but some of 
 his conclusions seem to have been arrived at without sufficient 
 thought. It is especially to t)e regretted that his theory of exhaus- 
 tion, framed at the outset, prevented the trial of remedial plans other 
 than the routine administration of stimulants and beef -tea. 
 
 The facts observed by Dr. Jaminet will be frequently referred to 
 in the following pages, care being taken to give him credit for all that 
 had not been anticipated by others. 
 
 CHAPTER SECOND. 
 
 THE NEW YOKK CAISSON. 
 
 Before the St. Louis Bridge was projected, a much more gigantic 
 work had been inaugurated at New York, and plans and specifica- 
 tions had been adopted which anticipated the leading features of the 
 work at St. Louis. To cross a stream 1,600 feet in width with a 
 single span was an idea never before entertained. But the difiicul- 
 ties were immensely increased by the fact that the towers to support 
 this immense structure had to be erected under circumstances that 
 rendered the usual methods for sinking piers impracticable. It was, 
 therefore, determined to employ the method by compressed air, and 
 caissons were constructed having the horizontal dimensions of the 
 proposed piers, which, on the New York side, were 102 by 172 feet. 
 Each caisson was in effect a wooden box turned bottom upward, the 
 interior space being 9 feet high. The roof of the New York caisson 
 (bottom of the box) was 22 feet thick, of solid timber bolted to- 
 
13 
 
 getlier, and was supported by frames riiuning from side tu side, which 
 frames, together with the edges of the box, were to sustain the vast 
 superincumbent weight, aided by the upward pressure of the con- 
 densed air within the caisson. Tlie area of the structure was equal 
 to seven building lots of 25x100 feet each 
 
 The caissons having been built on ways, were launched in the same 
 manner as a ship, and were towed to the points where the piers were 
 to be located. Courses of granite blocks were then laid upon the top 
 of the caisson, by which it was sunk until it rested upon the bed of 
 the river. Air was then forced into the chambers beneath by means 
 of engines upon the shore, until the water was entirely displaced, 
 and the river-bed left dry. The pressure was maintained at this 
 point, the engines working day and night. The workmen obtained 
 access to the chamber by means of two shafts w^hich extended above 
 the surface of the water. At the bottom of each shaft were two air- 
 locks, which were simply ante-chambers constructed of iron, into 
 which the men entered from the shaft, and, closing an air-tight door 
 behind them, admitted the compressed air from the caisson by means 
 of a cock, until the pressure in the lock reached the same degree as 
 that in the caisson, when a communicating door was opened, and the 
 men passed into the chamber below. In going out, the process was re- 
 versed, the compressed air in the lock being allow^ed to blow off 
 through a cock into the open shaft. The control of these cocks was 
 intrusted to men detailed exclusively for that work, and upon their 
 proper management depended ;^the comfort, if not the life, of every 
 one in the loc^. 
 
 By a very ingenious arrangement, which it is not necessary to de- 
 scribe here, the earth excavated from beneath the caisson was car- 
 ried up to the surface without affording opportunity for the air to es- 
 cape. In this way the earth w^as being constantly removed from un- 
 derneath the caisson, and the vast mass settled day by day down 
 through the gravel and quicksand, which formed the bed of the river, 
 until at a depth of 78 feet on the New York side, a solid foundation 
 was reached. In proportion as the caisson settled the masonry upon 
 it was built up, so that the top of the stone-work was alw^ays above 
 water. When a solid foundation had been reached, the interior of 
 the caisson was filled with concrete, and the 400,000 (?ubic feet of 
 timber was left buried nearly 80 feet below the surface, Avhere, prac- 
 tically indestructible, it remains as the foundation of the tower. 
 
 Of course the pressure of air required to keep the water out of the 
 caisson increased in exact proportion to the depth. Thus, at the 
 beginning of the work, the caisson being covered by forty feet of 
 water, the pressure was about eighteen pounds to the square inch, 
 while at the close of the Avork it stood at thirty-six pounds. 
 
14 
 
 The air-locks were connected with tlie surface of the pier b}^ means 
 of a spiral stairway within the shaft. Ascending this was found to 
 be exceedingly fatiguing as the depth increased, and the stair in one 
 of the shafts was finally replaced by a steam elevator. 
 
 Looking upon it merely from a sanitary point of view, I regard it 
 as a serious mistake to have placed the air-locks at the bottom 
 instead of at the top of the shafts, as by that arrangement the men 
 were compelled to make a fatiguing ascent at the moment when the 
 circulation was embarrassed and the system unstrung by the sudden 
 removal of the pressure. All testimony is agreed upon the ease, on 
 the one hand, with which exertion is supported while in the com- 
 pressed air, and upon the unfitness of the system, on the other hand, 
 to bear even the slightest fatigue during the period immediately fol- 
 lowing the change to the normal atmosphere. These considerations 
 should render the rule invariable that the air-lock is to be placed at 
 the top of the shaft, unless an elevator is employed. In this view I 
 am sustained by all the engineers connected with the work. 
 
 The caisson was lighted by gas supplied by means of a force-pump. 
 The combustion of the gas, together with the breathing of the work- 
 men, gave rise to the formation of a large quantity of carbonic acid. 
 It soon became evident, that the amount of air which was required to 
 supply the leakage and keep up the requisite pressure was not ade- 
 quate to maintain a healthy standard of purity in the air respired. 
 This conclusion, arrived at by observation and calculation, was con- 
 firmed by trial. A rough, but satisfactory, test was supplied by tak- 
 ing a bottle of lime-water into the caisson and passing the air through 
 the water by means of an ordinary flexible rubber syi'inge. It was 
 found that a few compressions of the bulb were suflicient to give the 
 water a decidedly milky hue. This method has the advantage over 
 that employed by Dr. Jaminet, viz. , merely shaking an open bottle 
 containing lime-water — that it constantly brings new portions of air 
 into contact with the fluid. 
 
 By increasing the number of compressors by which the air was 
 supplied, (the excess of air escaping beneath the edge of the caisson,) 
 the atmosphere was brought to such a degree of purity as to contain 
 only one-third of one per cent, of carbonic acid, as I determined hy 
 actual analysis. This amount of vitiation was found not to affect the 
 men unfavorably. To maintain this standard, however, nearly 
 150,000 cubic feet of au* were required per hour. 
 
 The number of men employed at one time in the caisson varied 
 from fifty to one hundred and twenty-five in the day time, and from 
 fifteen to thirty during the night. At first the time was divided into 
 two " shifts " of four hours each, separated by an interval of two 
 hours. As the depth increased the liours were reduced, until at last 
 
15 
 
 the two shifts comprised but four hours, dividetl by a four hours" 
 interval. 
 
 It was not until the pressiu'e had reached about twenty-four pounds 
 that any serious effect upon the men ^vas obseryed. At this time I 
 began my daily attendance of from one to three hours at the bridge. 
 The first step was to prepare a set of printed rules, copies of which 
 were posted conspicuously. These rules were as follows : 
 
 1st. — Xeyer enter the caisson with an empty stomach. 
 2d. — Use as far as possible a meat diet, and take warm coffee 
 freely. 
 
 od. — Always put on extra clothing on coming out, and avoid ex- 
 posure to cold. 
 
 4th. — Exercise as little as maybe during the first hour after coming 
 out, and lie down if possible. 
 5tli. — Use intoxicating liquors spai'ingly ; better not at all. 
 6th. — Take at least eight hom's' sleep every night. 
 7th.— See that the bowels are open every day. 
 8th. — Xever enter the caisson if at all sick. 
 
 9th. — Report at once at the office all cases of illness, even if they 
 occur after going home. 
 
 I next subjected all the men to an examination intended to exclude 
 all who were suffering from heart or lung disease, and those en- 
 feebled by age or intemperance. All new men thereafter were re- 
 quii-ed to pref ent a permit signed by me before they were allowed to 
 enter the caisson. Though but few were actually rejected, the 
 knowledge that they would be examined, doubtless deterred many 
 who were not sound from applying for work. The personnel was 
 therefore of the best, as it then appeared. Subsequent experience 
 would, however, have modified my choice materially. 
 
 On my recommendation a cup of good coffee was served to each 
 man immediately upon leaving the caisson. It appeared to relieve, 
 in a measure, the nervous prostration which marked the return to the 
 open air ; and possibl}^ \)y the effect w^hich coffee is known to have, 
 it may have done something, also, to check the tendency to too rapid 
 tissue-change. 
 
 A large room in the j'ard was fitted up with bunks and benches, 
 which afforded the men an opportunity of resting while the changes 
 were going on in the system which were required to bring it into its 
 normal condition after coming up. Connected with this room were 
 conveniences for hot and cold bathing, and also lockers in which each 
 man kept a change of dry under-clothmg, to be put on inmiediately 
 
10 
 
 on coming up. Each man was supplied by the company with a pair 
 of long rubber boots, which were rendered necessary by the work re- 
 quiring them to stand more or less in the water. 
 
 The physical conditions to which the men were subjected in their 
 work were very peculiar. In the first place, in passing through the 
 lock in going dowm, there "was a very sudden rise of temperature from 
 the condensation of the air This rise amounted to upwards of 30" 
 F. in many cases, and not infrequentl}^ when the outside tempera- 
 ture was low, to 50° or 60°. This change in the temperature was 
 coincident with an increase of atmospheric pressure of from 18 to 
 36 lbs. to the square inch. At the same time the men passed from an 
 atmosphere of the usual dryness to one saturated or super-saturated 
 Avith moisture. The labor required in the caisson was not unusually 
 severe. After from two to four hours passed in the compressed air, 
 the men repaired to the locks, where in the space of from seven to 
 fifteen minutes the pressure was reduced to the normal standard. 
 As the result of the expansion of the air in the lock, the temperature 
 fell as rapidly as it rose in the former case. This, which was felt to 
 be a serious inconvenience in the Brooklyn caisson, was remedied on 
 the New York side by surrounding the interior of the lock with coils 
 of pipe heated by steam. T)?e steam Avas shut off at all times except 
 while locking out. 
 
 The moisture of the atmosphere of the caisson, referred to above, 
 was caused partly by the ' ' water-packing " used in the condensers 
 which supplied the air, and partly by the water with which the 
 soil underneath the caisson was saturated. 
 
 From the 25th of January, 1872, when I assumed medical charge 
 of the men, until the 31st of May, when I resigned the position, 110 
 cases of sickness occm-red which were fairly due to the compressed 
 air, and were of sufficient severity to come under treatment. Of 
 these, three proved fatal. 
 
 The sick were treated in the first instance at the yard, where 
 a room was set apart as a temporary hospital. Cases occurring dur- 
 ing ni}^ absence were treated by the engineer on duty, according to 
 a specified plan ; or, if the case was severe, I was summoned. 
 Serious cases were ultimately sent to the public hospitals or to their 
 homes. 
 
 The ages of the men ranged from 18 to 50. They were of almost 
 all nationalities, but I did not find that any sensible difference in 
 ability to bear the work resulted from nativity, as observed by Pol. 
 
 The habits of many of the men were doubtless not favorable to 
 health, but everything which admonition could do, was done to 
 restrain them from excesses. Many of them slept in crow^ded lodging- 
 houses, where the beds or bunks were arranged in tiers, one above 
 
17 
 
 the other ; iu rooms in which there was scarcely an attempt at venti- 
 lation. One of them fell a victim to spotted fever, contracted from 
 such surroundings, and his death was at once ascribed by his com- 
 rades to the effects of the condensed air. 
 
 Serious inconvenience M'as occasioned to the men in the caisson by 
 the large amoimt of unconsumed carbon from the gas, which floated 
 in the air in the form of smoke. The inhalation of this produced 
 more or less irritation of the air-passages, and gave rise to a very 
 characteristic black expectoration. This continued for an astonish- 
 ingly long period after the work in the caisson was terminated. At 
 the time of my writing, nearly six months after the work was com- 
 pleted, some of the men are still coughing up sputa, streaked with 
 black. Where this carbon could have been lodged for so long a 
 period, is a question which I am not prepared to answer. 
 
 The smoking of the gas was found by some experiments of Mr. 
 Collingwood, one of the engineers, to be due to the comparative 
 immobility of the compressed air, which prevented the formation of 
 the currents necessary to bring new supplies of oxygen to the flame. 
 By reducing the aperture of the burners, and at the same time giving 
 it such a form that the gas escaped in a thin sheet, a relatively great- 
 er surface was secured for contact with the air. This obviated almost 
 entirely the tendency to smoke, and added also to the illuminating 
 power of the gas. 
 
 The sinking of the caisson was begun on the 13tli of December, 
 1871, and the filling in with concrete was completed on the 20th of 
 July, 1872 : the duration of the submarine work being 221 days. 
 
 During thia^eriod I was in the habit of frequently entering the 
 caisson, remaining from one to two hours at a time. Yet in my case, 
 with the exception of occasional slight pain in the maxillary sinuses, 
 not the least inconvenience was experienced. 
 
 CHAPTER THIRD. 
 
 EFFECTS OF COMPRESSED AIR. 
 
 The effects of a highly condensed atmosphere upon the sj^stem 
 may be divided into those which are physiological or consistent with 
 health, and those which are pathological, and constitute or induce 
 disease 
 
 The physiological effects will be considered according to the organs 
 or functions in which they are exhibited. 
 
 Effect on the Hearing. — It is a law of acoustics that within the 
 limits of mobility the denser the medium through which the sound 
 waves are communicated, the larger the wave, and therefore the 
 
 B 
 
18 
 
 louder the sound. This supposes, of course, that the ear itself re- 
 mains under normal conditions. Such, however, is not the case 
 when the observer is in a highly condensed atmosphere. The un- 
 usual pressure upon all parts of the auditory apparatus opposes a 
 mechanical obstacle to the freedom of vibration, which is essential 
 to perfect hearing * Hence, although larger sound waves may strike 
 upon the ear-drum, feebler impressions are communicated to the 
 auditory nerve, and the sound appears to be fainter than in the opeij 
 air. Thus, by repeated experiments, I found that a watch that could 
 be heard distinctly at a distance of 18 inches in a very noisy place in 
 the open air, could not be heard at a greater distance than two inches 
 in the comparative silence of the caisson. 
 
 At the same time the velocity of the waves of sound is greater, and 
 hence the pitch is higher. A deep bass voice is changed to a shrill 
 treble, and the prolonged, heavy sound of a blast is so modified as to 
 resemble the sharp report of a pistol. 
 
 This modification of sound is very striking, and is almost the only 
 thing to remind the casual observer that he is moving about in an 
 atmosphere three or four times as dense as that to which he is accus- 
 tomed. 
 
 A curious fact, noticeable under these circumstances, and one which 
 was long ago obser^^ed in diving-bells, is that it is impossible to 
 whistle. The utmost effort of the expiratory muscles is not suffi- 
 cient to increase materially the density of the air in the cavity ot the 
 mouth, and hence on its escape there is not sufficient expansion to 
 produce a musical note. A similar difficulty, though in a less degree, 
 is experienced in speaking, and for this reason protracted conversa- 
 tion is very fatiguing. 
 
 Effect upon Respiration. — In a highly compressed air, the frequency 
 of the respiration is increased. Dr. Jaminet gives the rate as 21 per 
 minute, with a pressure of 33 lbs., which accords with my own ob- 
 servations. He ascribes this increase of three or four per minute to 
 an increased absorption of oxygen. Experiments show, however, 
 that simply increasing the supply of oxygen, the frequency 
 
 of respiration instead of increasing it. The true explanation, I 
 think, is to be found in the fact that the quantity of carbonic acid 
 held in solution by blood, as by water, is in proportion to the pressure 
 to which the gas is subjected ; and hence with the pressure existing 
 in the caisson, the elimination of carbonic acid from the blood would 
 not be as perfect as under normal circumstances, unless the air in the 
 lungs were more frequently changed. As observed by Frangois and 
 Dr. Jaminet, the depth of the inspirations is also increased. With 
 
 * An analogous fact was observed by Foley, viz., that his watch invariably lo>it 
 time when taken into the caisson, thus showing that the movements of the ))al- 
 ance-wheel were less free in the compressed than in the normal air. 
 
19 
 
 the view of appreciating thie amount of increase of the respiratory 
 movements, as well in amplitude as in frequency, I devised the fol- 
 lowing plan : By a very simple contrivance attached to a steel band 
 placed around the chest, a measuring tape was made to traverse with 
 each inspiration a distance corresponding to the increase in the cir- 
 cumference of the chest. The aggregate distance traversed in a given 
 time was made the standard of comparison, and of course indicated 
 the combined frequency and amplitude of the respirations. 
 
 A number of trials with this instrument made upon myself in the 
 open air, gave a very uniform result of 1^ inches of tape unwound 
 every two minutes. On repeating the experiment in the caisson 
 under a pressure of 33 lbs., 2f inches were unwound in the same 
 time. 
 
 Bffect upon the Circulation. — It has been shown by numerous ob- 
 servers that under a slightly increased pressure, such as is employed 
 in compressed air-baths, the pulse loses in frequency from the first. 
 Tills is doubtless due to an increased absorption of oxygen by the 
 blood, which thus affords a sufficient supply to the tissues without 
 the necessity of keeping up the usual activity of the circulation. In 
 the course of some experiments undertaken nearly four years ago, I 
 demonstrated that the same effect results under a normal pressure 
 from adding oxygen to the air inhaled. But as the pressure in- 
 creases, the question is transferred from the domain of chemistry to 
 that of mechanics. The condensation of the tissues from the pres- 
 sure to which they are subjected, and the consequent narrowing of 
 the vessels, oppose a physical obstacle to the circulation, which is felt 
 before the blood has time to become sm-charged with ox3^gen, and 
 while there is still a necessity for an active cii-culatiou. The labor 
 of the heart is thus increased, and its action, in consequence, excited. 
 I have frequently seen the pulse rise to 120 immediately upon enter- 
 ing the caisson, where the pressure was from 30 to 35 lbs. to the inch. 
 
 But after the lapse of a period varying in different cases from half 
 an hour to two hours, the pulse falls back to its normal standard, or 
 even, it maybe, below it.* The blood has now become saturated 
 with oxygen, and consequently a less active circulation is demanded. 
 
 Doubtless, if the pressure were very gradually admitted, the pre- 
 liminary rise in the pulse would not take place, the favorable chemi- 
 cal action keeping in advance of and counteracting the unfavorable 
 mechanical conditions. 
 
 The effect of high atmospheric pressure upon the volume of the 
 pulse is always, according to my observation, to diminish it. This is 
 easily accounted for by the pressure exerted upon the arterj', which 
 prevents its yielding readily to the expanding force of each successive 
 
 * My experience in tliis corresponds precisely with that of Dr. Jaminet. 
 
20 
 
 wave of blood. Hence the pulse is small, hard, and wiry. These 
 characteristics are independent in a great degree of the frequency of 
 the beat, although as the heart recovers from the irritable con- 
 dition into which it is thrown by the sudden increase of the pressure, 
 and settles down, so to speak, more calmly to its work, it contracts 
 with more force, and the pulse gains somewhat in volume. These 
 changes in both the frequency and fullness of the pulse are well shown 
 in the annexed tracings, taken in the Brooklyn caisson. The upper 
 line represents in each case the normal pulse, the lower line that in 
 the compressed air. 
 
 The difference in the readiness with which the process of adapta- 
 tion to an increased pressure is accomplished in different persons is 
 shown by the pulse-rate of eleven men taken an hour and a half after 
 going into the caisson when the pressure was thirty-five pounds. The 
 figures are arranged in the order of frequency. 
 
 116—116—106—104—96—92—88—76—74—68—52. 
 These figures give an average of ninety. On another occasion, with 
 a pressure of thirty-two pounds, and a sojourn in the caisson of two 
 and a half hours, the average was eighty. Whether a longer expo- 
 sure to the same jn-essure would have produced a further decline in 
 the frequency of the i)ulse is a question which the hours for working 
 did not allow me to determine. 
 
21 
 
 It is remarkable that the wide variations in the pulse-rate above 
 mentioned were not accompanied by any symptoms appreciable to 
 the individual. A man with a pulse of fifty-two, and another with 
 one of one hundred aftd sixteen, felt equally well, and each was en- 
 tirely unconscious of anything unusual in the heart's action. 
 
 The effect of the pressiu'e upon the cutaneous vessels is shown by 
 the pallor of the face, Avhich is very marked, and continues for fif- 
 teen or twenty minutes after leaving the caisson. The hands, too, 
 feel shrunken, and the palmai* surface of the fingers is often shriv- 
 elled, as if soaked in water. The pressure acting upon all sides of the 
 fingers empties them to a considerable extent of blood, rendering the 
 skin apparently too large for them. The veins, too, on the back of 
 the hand seem to be effaced. 
 
 This absence of blood from the surface implies necessarily an ex- 
 cess in the interior of the body, where the effect of the pressure is not 
 as great. This point will come up again in considering the pathology 
 of the Caisson Disease. 
 
 Effect upon Tem-perature. —In none of the reports upon the effects 
 of high pressure as employed for engineering purposes, have I been 
 able to find any records of temperature. J. Lange,* however, found 
 that under the comparatively slight pressure which is used as a reme- 
 dy, the temperature of the body suffered a slight decrease. This is, 
 no doubt, due to an increased absorption of oxygen, which has been 
 shown by Mr. Savory and also by experiments of my own to produce 
 this effect. 
 
 During tl^e work in the New York caisson when the pressure was 
 about 32 l6s. , I took the temperature of seven of the men an hour 
 and a half after entering the caisson, and found that it averaged 
 99.6® F., exactly one degree above the normal standard. At first I ac- 
 cepted this as the result of the increased interstitial change so strong- 
 ly insisted upon b}' Dr. Jaminet, but subsequent observation led me 
 to interpret it differently. 
 
 The temperature of the body in health is kept at about 98.6° F., by 
 the constant evaporation from the surface. But in the caisson, as 
 already mentioned, the air was always nearly or quite saturated with 
 moisture, so that evaporation from the surface must have been prac- 
 tically suspended. With the temperature of the air at 76'', as it was 
 at the time of the observations, and the men engaged in severe labor, 
 it is easy to see how the absence of the cooling process of evapora- 
 tion from the surface would lead to a rise of one degree of the ther- 
 mometer. This view is strengthened by the result of three observa- 
 tions on a subsequent occasion, when the temperature in the caisson 
 stood at 81®, instead of 76". The average in this instance Avas 101®. 
 
 * Vivenot. 
 
22 
 
 A rise of tive degrees in the temperature of tlie air could not sensibly 
 affect the rapidity of tissue-change, but if not counteracted by evap- 
 oration from the skin, it would soon tell upon the temperature of the 
 body. 
 
 The influence of the hygrometric condition of the atmosphere 
 upon the temperature of the body is a matter of daily observation. 
 On a clear, dry day, with a high barometer, we are surprised to find 
 the thermometer indicating a temperature much higher than our sen- 
 sations would lead us to expect, while on the contrary, on a cloudy 
 day, with a low barometer, we can scarcely persuade ourselves that 
 the temperature is not many degrees higher than the thermometer in- 
 dicates. In the dry, clear air of New Mexico I have supported a tem- 
 perature of 110°, without inconvenience, while in the humid atmos- 
 phere of the Florida Keys I have found it almost unbearable at 86''. 
 
 Effect upon the Perspiratory Function. — Several writers have ob- 
 served that it is immediately remarked by every one entering a 
 caisson that the secretion from the skin is apparently immensely 
 increased. It is noticeable even when the temperature of the air is 
 moderate, but as this increases it becomes a very serious annoyance. 
 The clothing quickly becomes saturated, which, besides the discom- 
 fort it occasions, exposes to gieat danger of taking cold on going out 
 into the open air. 
 
 But a little examination served to show me that in the New York 
 caisson, at least, there was really no increase of the secretion from the 
 skin, but that, instead of evaporating, the moisture accumulated upon 
 the surface, and thus simulated excessive sweating. This was owing 
 to the moist condition of the atmosphere already mentioned, which 
 rendered the drying of the surface by evaporation impossible. The 
 atmosphere possessed to an extreme degree the quality of " niuggi- 
 ness," and the apparently profuse perspiration was merely an exag- 
 geration of what we suffer from in very damp weather, even though 
 the temperature be not extreme. 
 
 So far from the perspiratory glands being stimulated by the density 
 of the atmosphere, it is probable that the anaemia of the skin already 
 described, as resulting from the pressure upon the surface, would 
 tend to lessen the secretion by diminishing the supply of blood to the 
 glands. 
 
 That there is not an imdue amount of fluid carried off thi'ougli the 
 skin, is shown by the absence of thirst so generally remarked. 
 
 The foregoing explanation of the apparent increase of perspiration 
 is important, as it bears upon the theory of excessive waste of tissue, 
 in which the perspiration is supposed to aid. 
 
 Effect upon Digestion. — Nearly all authors who have written upon 
 the effects of compressed air agree in stating that for a time, at least, 
 
23 
 
 it increases the appetite to a remarkable extent. Indeed this is one 
 of the first and most favorable results observed where compressed air 
 is applied remedially. With this experience my own observations in 
 the main agree. It was frequently remarked by the men working in 
 the New York caisson that their work made them unusually hungry, 
 that they " could not get enough to eat," etc. Of course, it was not 
 possible to obtain any exact data as to the relative amount of food 
 consumed, but from careful inquiries I arrived at the conclusion that 
 it was considerably in excess of Avhat is usual in the case of men 
 engaged in similar labor in the open air. Still, there were many 
 exceptions to the general rule, especially among those Avho had been 
 long engaged upon the work, and whose general tone was beginning 
 to deteriorate. Among these, loss of appetite Avas often complained of. 
 
 The fact of this generally increased appetite seems to point to an 
 increased Avaste of tissue, to be supplied by a greater consumption of 
 food. An increased absorption of oxygen such as Ave assume to take 
 place, seems from the observations of several authorities* to imply 
 greater activity of tissue-change as the ultimate result. But in this 
 case I think it is scarcely safe to accept this explanation at once as 
 conclusive and sufficient. It may aa^cII be questioned whether during 
 the actual sojourn in the caisson the functions of digestion, absorp- 
 tion, and assimilation proceed normally under the wide departure of 
 the system from its natural conditions. If it could be shoAA'n that a 
 considerable portion of the food taken before entering the caisson is 
 but imperfectly digested or assimilated, the subsequent hunger Avould 
 be readily accounted for. I am not aware that this point has ever 
 been investigated, but I can scarcely believe that such an increase of 
 appetite as is described could depend Avholly upon increased inter- 
 stitial change without giving rise to marked elevation of temperature 
 and other SA'mptoms denoting unusual chemical activity. On the 
 contrary, I think it highly probable that an examination of the de- 
 jecta would shoAv them not to be entirely exhausted of nutritious 
 material. At all events, until this point is subjected to rigid tests, it 
 Avill be unsafe to regard the amount of food consumed as a measure 
 of the metamorphosis of tissue. 
 
 If the metamorphosis of tissue is really greatly accelerated through 
 the influence of compressed air, it should be apparent in a more 
 prompt healing of Avounds. The folloAving experiment Avas intended 
 to test this point : 
 
 Four pigeons Avere selected, as much alike as possible in size and 
 vigor. Under the Aving of each a Avound Avas made by removing a 
 circular piece of the integument about half an inch in diameter. 
 Two of the pigeons AA^ere then sent down into the caisson, the other 
 * " New York ;Nreflical Journal." April, 1870. 
 
24 
 
 two being retained in the hospital on the wharf. The conditions in 
 other respects were the same. At the end of six days the wounds in 
 the two below were perfectly healed. Of the two above, in one the 
 wound was perfectly healed, while in the other it was still covered 
 by a scab, which fell off two or three days later. 
 
 The result of this experiment w^ould not indicate any considerable 
 difference in the activity of the vital processes. I may remark that 
 the w^orkmen never spoke of the wounds or injuries they received as 
 healing more rapidly than when working in the external air. 
 
 Effect npon the Urinary Secretion. — Dr. Jaminet, in his observa- 
 tions at St. Louis, found that the amount of fluid secreted by the 
 kidneys was very much increased, in some instances nearly doubled, 
 while the specific gravity was but little, if at all, below the usual 
 average. This shows that the solid matter excreted was also in much 
 greater quantity than usual.* But I cannot agree with him in attrib- 
 uting this exclusively to the excessive waste of tissue from over-oxyd- 
 ation of the blood. The explanation is to be found, I think, chiefly 
 in the fact that the skin, as already stated, performs its function 
 very imperfectly, owing to the impossibility of evaporation from the 
 surface when the air is already loaded with moisture, and hence a 
 portion of its duty is forced ^ipon the kidneys, organs always ready 
 to act vicariously for the skin or the mucous surfaces. 
 
 Furthermore, the excretion of a large amount of urea indicates a 
 relatively deficient oxydation of tissue, and is one of the characteris- 
 tics of those diseases in which respiration is suddenly embarrassed, 
 as, for instance, pneumonia. 
 
 Another circumstance not to be lost sight of, is that the pressure 
 upon the surface acts mechanically to congest all the abdominal vis- 
 cera, and that congestion of the kidneys, within physiological limits, 
 produces increased secretion of urine. 
 
 From w^hat precedes it will be inferred that I am not willing to ac- 
 cept the view which practically sets no limit to the amount of oxygen 
 that the system will appropriate in a sufficiently condensed atmos- 
 phere. Even if absorbed by the blood, it does not follow that, the 
 excess of oxygen is received into the normal vital relations with the 
 tissues. It may be held in simple compulsory solution in the blood, 
 as in any other liquid ; it may even give rise to chemical changes in 
 the blood, and solid tissues as in dead matter, and thus act as a poison, 
 as asserted by M. Bert,t but we have no w^arrant for believing that it 
 so acts as to cause the removal of particles not yet eifete, and which 
 but for this would have remained normal active constituents of the 
 
 * These oV)servations accord with those of Foley, J. Lange, Pol, Pravaz, and 
 others, 
 t L'Institut, July i?, 1872 
 
25 
 
 body. Behind mere chemical action lies a vital principle in accord- 
 ance with which each molecule is born, as it were, into the economy, 
 reaches maturity, performs its function, becomes effete, and is suc- 
 ceeded by a new molecule ; and to break in upon this order is to 
 strike at the very essence of life. 
 
 I do not intend by this to deny that an atmosphere highly oxygen- 
 ated, either by the addition of oxygen or by compression, is capable 
 of accelerating the vital processes within certain limits. I only 
 contend that these limits correspond with the extreme limit of 
 physiological demand — that the capacity of the system to appropriate 
 and use oxygen has a definite relation to the possible wants of the 
 system under natural conditions. For a contingency beyond these, 
 nature has made no provision. 
 
 CHAPTER FOURTH. 
 
 PATHOLOGICAL EFFECTS. 
 
 The pathological effects of high atmospheric pressure comprise 
 certain phenomena easily explained upon mechanical principles, and 
 in addition to these, a group of symptoms, having a definite relation 
 to each other, and constituting a specific affection, which, from the 
 peculiarity of its origin, I propose to call the Caisson Disease. 
 
 The affections, which are of a purely mechanical nature, relate to 
 the cavities communicating with the nasal passages, such as the ears 
 and the fronlal and maxillary sinuses, etc. 
 
 Affections of the ears are mentioned by nearlj' every writer on the 
 subject of compressed air, and are extremely common. They 
 depend, for the most pai't, upon closure of the Eustachian tubes, by 
 which communication of the cavity of the middle ear with the 
 external air is cut off. The men under my charge Avere warned most 
 strenuously not to go into the lock unless they were able, when 
 holding the nose and blowing forcibly, to feel the air enter both 
 ears, thus insuring that the tubes were per\ious. Nevertheless, cases 
 often occurred in which this precaution was neglected, and the indi- 
 vidual was, as a consequence, " caught in the lock," unable to 
 
 change his ears. " This inability to equalize the pressure upon the 
 two sides of the ear-drum, caused extreme pain, and sometimes 
 entailed serious results. The effect is two-fold. The pressure upon 
 the outside of the drum being greater than upon the inside, the mem- 
 brane is pressed inward with a force, which, if it does not produce a 
 rupture, at least causes a degree of tension which so delicate an 
 organ as the ear is not fitted to bear \\ith impunity, and which may 
 be the starting point of an acute inflammation. (See Case I., p. 43.) 
 
 4 
 
26 
 
 But the pressure may be so great as to rupture the drum at once, as 
 in Case II., p. 43. 
 
 When there is continued exposure to the effect of compressed air, 
 with closure of the Eustachian tube, the structures within the cavity 
 of tlie tympanum not being acted upon by the increased pressure, are 
 placed relatively in the same position as the skin under a cupping- 
 glass, and the sama result follows, viz., intense congestion, which 
 may, in this case, lead to inflammation. Indeed, the difference 
 in pressure within and without is much greater than in the case 
 of the cupping-glass, since in the latter it cannot exceed one at- 
 mosphere, while in the former it may be two or three atmospheres. 
 
 The stoppage of the Eustachian tube may very frequently be over- 
 come by forcing in air through the nose after the method described 
 by Politzer. In this way a great many of the men under my care 
 were enabled to continue their work, who otherwise could not have 
 done so, without incurring serious risk. This simple operation was 
 constantly called into requisition, as many as four or live of the men 
 sometimes presenting themselves in the course of my visit to have 
 their " ears blown out," and it rarely happened that they experienced 
 any difficulty afterward on entering the lock.* 
 
 Three cases of extreme deafness came under my notice, two of 
 them in laborers, and one in the person of a gentleman, who was ad- 
 vised by a physician to visit the caisson with the hope that he might 
 receive benefit from the action of the compressed air. In all these 
 cases the hearing was very much improved while in the caisson, but 
 on returning to the open air the former degree of deafness immedi- 
 ately returned. 
 
 A number of cases of otities are mentioned by Frangois, as occur- 
 ring under his observation during the sinking of the caissons at Stras- 
 burg.f His favorite remedy Avas oil of jasmine dropped into the 
 ear. He also employed leeches and fomentations. He condemns 
 catheterism of the tubes, on theoretical grounds, while admitting 
 that he had never employed it. 
 
 Pain, more or less severe, in the frontal or maxillary sinuses was 
 sometimes experienced. This w^as doubtless caused by a temporary 
 closure of the passage leading to the nasal cavity. In one case, in 
 which the frontal sinus was affected, the pain, though not severe, 
 was very persistent, continuing for several days. 
 
 In one case pain in the frontal sinus was felt as the pressure was 
 increasing in the lock, and again, and more severely, as the pressure 
 was reduced in returning to the open air. This latter pain was ac- 
 companied by a discharge of bloody mucous from the nose. In this 
 case there was doubtless closure of the passage into the sinus, thus 
 
 • I am under obligations to Dr. Roosa for valuable hints in reference to the treat- 
 ment of these cases, 
 t See page 9. 
 
27 
 
 preventin<^ the equalization of the pressure, and giving rise to the 
 pain first felt. There resulted also congestion of the lining mem- 
 brane, followed by an increased flow of mucous and extravasation of 
 blood. But in the course of the two hours passed in the caisson, the 
 air gradually filtered through the obstruction, and when the outside 
 pressure was removed, the air thus imprisoned forced a way out, car- 
 rying before it the mucous and blood that had accumulated in the 
 sinus. (See Case IV., p. 43.) 
 
 It becomes an interestmg question what degree of condensation of 
 this atmosphere will prove directly fatal. Dr. Richardson, of Lon- 
 don, told me recently that he had experimented largely upon this 
 subject, and that for the small animals which he had employed, such 
 as rabbits, cats, dogs, etc. , the limit of endurance seemed to be be- 
 tween six and seven atmospheres. He found, however, that the re- 
 sult varied widely, with comparatively slight variations of tempera- 
 ture, such as would have no appreciable effect upon vitality under 
 other conditions. 
 
 CHAPTER FIFTH. 
 
 THE CAISSON DISEASE. 
 
 Definition. — A disease depending upon increased atmospJieric pres- 
 sure, hut always developed after the pressure is removed. It is charac- 
 terized hy extreme pain in one or more of the extremities, and sometimes 
 in the trunk, and which may or may not be associated icith epigastric 
 pain and vomiting. In some cases the pain is accompanied by paralysis 
 more or less* complete, lohich may be general or local, but is most fre- 
 quently confined to the lower half of the body. Cerebral symptoms, 
 such as headache and vertigo, are sometimes present. The above symp- 
 toms are connected, at least in the fatal cases, loith congestion of the 
 brain and spinal cord, often resulting in serous or sanguineous effusion, 
 and icith congestion of most of the abdominal viscera. 
 
 SYMPTOMS. 
 
 Neuralgic Pains. — These constitute in general the first and most 
 characteristic symptoms, and are very seldom absent. The accession 
 is often very abrupt, as if the patient "had been struck by a 
 bullet." At other times the pain is slight at first, but rapidly increases 
 in intensity. In well-marked cases the suffering is extreme, men of 
 % the strongest nerve being completely subdued by it. It is " as if the 
 
 flesh were being torn from the bones." The pain is usually of a 
 remittent or paroxysmal character, the exacerbations occurring at 
 short intervals, especially if the patient attempt to move. Though 
 usually designated as "cramps," these pains are rarely accompanied 
 by muscular spasms. They generally begin in one or both of the 
 
28 
 
 knees, shifting to the legs or thighs, and then perhaps creeping up 
 along the trunk to seize upon the shoulders and arms. Not unfre- 
 quently the severest pain is felt in the spine, and especially in the 
 lumbar portion. There is usually some degree of tenderness with the 
 pain, so that the patient will complain if friction be applied too 
 vigorously. There is also a painful stiifness in the affected limbs, 
 that precludes motion in the absence of actual paralysis. 
 
 In some cases, there are swelling and heat as well as tenderness, 
 indicating engorgement of the tissues, and this may persist for seve- 
 ral days, being followed occasionally by discoloration, as if from a 
 bruise. (Case VII., p. 44.) 
 
 Frangois mentions a case in which the engorgement was followed 
 by suppuration. In two of my cases, minute spots of extravasated 
 blood in the substance of the skin at the seat of pain, gave the sur- 
 face the appearance of being spattered with red ink. (Case XI., 
 p. 45.) 
 
 A curious case of the swelling of the mammary gland recurring- 
 each day is given among the Illustrative Cases, No. IX. FrauQoia 
 relates a similar instance. 
 
 The Pulse. — At the outset of the attack the pulse will differ 
 according to the time which has elapsed since leaving the caisson, 
 being, as a rule, quicker and more frequent in proportion as the time 
 is shorter. Dr. Jaminet observed that if the attack occurred imr.e- 
 diately after coming up, the pulse usually ranged from 95 to 115, 
 while, if it were delayed for half an hour, the pulse would be 
 slow — perhaps as low as 60. 
 
 But as these rates do not differ from those in healthy persons at 
 the same periods after leaving the caisson, they do not possess any 
 special significance in those taken sick. 
 
 The subsequent character of the pulse is simply indicative of the 
 general condition of the patient. 
 
 The Skin is usually cool at first, often of a slightly leaden hue, and 
 nearly always covered with a profuse cold perspiration, standing out 
 in beads upon the surface. This perspiration is very characteristic. 
 At first I supposed it to be owing to the excessive pain which the pa- 
 tient was suffering ; but subsequently it occurred in several cases in 
 which the pain was slight or entirely absent. (See Case VI.) I was, 
 therefore, inclined to attribute it to a relaxation of the cutaneous 
 capillaries through some nervous agency analagous in its action t<> 
 what we see in cases of extreme terror, and having its origin in the 
 general disturbance of the nervous system which chai-acterizes the 
 disease. 
 
 In several instances in which I ascertained the temperature in the 
 axilla, it was found to be normal. 
 
29 
 
 Epigastric Pain and Vomiting. — Pain at the pit of the stomach, 
 usually, but not always, attended by vomiting, is of frequent occur- 
 rence. It occurred in 24 per cent, of my cases. This is a much 
 smaller percentage than that observed by Dr. Jaminet, who found 
 the gastric symptoms to be present in 66 out of 77 cases. This may 
 be owing to the pressure being greater at St. Louis than at New York, 
 nearly all of Dr. Jaminet's cases occurring under a pressure of 40 
 lbs. and upward, while the pressure at New York did not rise above 
 36 lbs. 
 
 The pain in the epigastrium, if not relieved by treatment, is gener- 
 ally followed within a brief period by vomiting, which may continue 
 with great persistence even after the pain has ceased. In most cases, 
 however, the vomiting is limited to the ejection of the contents of 
 the stomach. 
 
 In a few instances I observed the occurrence of vomiting without 
 the usual preceding pain. In these cases there was also dizziness, in- 
 dicating that the vomiting was of cerebral origin. 
 
 Paralysis — This occurred to a greater or less degree in 47 out of 
 77 cases observed by Dr. Jaminet. This is at the rate of 61 per cent. 
 At New York it occurred in only about 15 per cent, of the cases ; 
 the difference being due, no doubt, to the difference of pressure. 
 The paralysis affects most frequently the lower half of the body, 
 but it may include the trunk or one or both arms. In rare instances 
 the arms alone are affected. The paralysis usually comes on a short 
 time after the beginning of the pains, but it may occur where there 
 is very little if any pain. (Case XXV.) It affects sensation as well 
 as motion. The patient does not, however, obtain relief from his 
 suffering, since the pain in the limbs will continue after pain from 
 other sources is no longer felt. Thus a leg, for example, may be en- 
 tirely insensible to pricking or pinching, while at the same time it is 
 the seat of extreme suffering. In fact, the neuralgic pain and the 
 paralysis seem to be so far independent of each other, that either 
 may exist separately as well as both together. 
 
 The degree of paralysis may vary from mere weakness of the 
 limbs, with slightly impaired sensation, including a loss of "hold 
 upon the ground " in walking, to complete loss of motion and sensa- 
 tion in the affected part. Even the minor degrees generally involve 
 the bladder, and in two or three of my cases the paralysis, after the 
 first day or two, was confined to this organ. 
 
 Cerebral Symptoms. — Symptoms of a transient character are often 
 observed, which have their origin in the brain. They consist of 
 headache, dizziness, double vision, incoherence of speech, and some- 
 times unconsciousness, the last from syncope. They are usually of 
 very short duration, passing off in a few hours. In the fatal cases. 
 
30 
 
 however, a condition of profound coma is the usual forerunner of 
 death. The occurrence of this symptom leaves but little hope of the 
 patient's recovery. 
 
 Prognosis. — The duration of the Caisson Disease varies from three 
 or four hours to six or eight days. When paralysis takes place, this 
 may continue for weeks, or it may pass off within twelve hours. 
 The cases marked only by neuralgic pains do not generally last more 
 than twelve hours, though some continue five or six days. 
 
 Death occurs only in cases which are severe from the first, and are 
 marked by symptoms of serous or sanguineous effusion about the 
 brain or cord. 
 
 Morbid Anatomy. — The constant lesion in fatal cases of Caisson 
 Disease is congestion of the brain or spinal cord. This congestion 
 may be evenly distributed, or it may vary in intensity in different 
 localities. This is especially true as regards the cord. The conges- 
 tion affects both the meninges and the substance of the brain or 
 cord. In some instances extravasation of blood takes place, as in 
 Case XXVI., chapter 6. In most of the published cases there was 
 found also more or less serous effusion in the arachnoid. 
 
 The tissues of the scalp and those surrounding the spinal column 
 are sometimes engorged. Dr. Jaminet describes a case in which the 
 tissues over the spine were congested, the vascularity increasing 
 regularly as the dissection proceeded deeper toward the vertebral 
 column. 
 
 When sufficient time elapses before death, there may be softening 
 of the brain, occurring in spots. This is probably due to occlusion 
 of the vessels by coagula formed during the primary congestion. 
 
 Congestions also occur in other localities, and especially in the 
 solid abdominal viscera. The liver and spleen have been found 
 engorged in nearly every case. The kidneys, too, are usually con- 
 gested, and in several cases described by Dr. Jaminet, clots of blood 
 were found extravasated in the organ. 
 
 The mucous membrane of the stomach, intestines, and bladder is 
 often found injected and marked with ecchymotic patches. 
 
 The lungs, in cases of true Caisson Disease, seldom present any 
 other change than simple hypostatic congestion. 
 
 Pathology. — It iB probable that the pathology of this disease is not 
 entirely uniform in all cases. Doubtless, the chief element in it is 
 the congestions already described, and especially of the brain and 
 spinal cord. The mechanism, therefore, of these congestions, be 
 comes a subject of paramount importance. 
 
 It is obvious that if the blood were exposed to an equal pressure in 
 all parts of the body, there would be no change in its distribution. 
 
 * Physical Effects of Compressed Air. P. 20. 
 
31 
 
 It is equally clear tlint the blood, if free to move, will pass from a 
 place where the pressure is greater to one where it is less. The 
 body is made up of structures of different densities, and presenting a 
 varying resistance to compression. But permeating these structures 
 in every direction are vessels in perfect communication throughout 
 the entire system, and filled with a mobile fluid, which is free to 
 change its locality in obedience to any force which is brought to act 
 upon it. Now, w^hen the surface of the body is subjected to an 
 even pressure on all sides, the tendency is to a distribution of this 
 pressure toward the centre. If the body were composed entirely of 
 solids, this could be effected only by the compression of those solids, 
 and a point w^ould very soon be reached where the resistance w^ould 
 balance the compressing force, and the parts lying more toward the 
 centre w^ould remain unaffected. But the presence of a fluid in the 
 structures, with free channels in w^hich to move, changes all this. 
 While the solid tissue resists compression, the fluid blood retreats 
 from the surface to the centre, and accumulates there until an equi- 
 librium of pressure is produced. 
 
 Hence we deduce the law, that under high atmospheric pressure 
 the centres will be congested at the expense of the periphery. 
 
 But, aside from location, vessels coursing through dense and resist- 
 ing organs, will be less exposed to external pressure than those pass- 
 ing through soft and yielding structures. Hence a second law% that 
 firm and compact structures will be congested at the expense of those 
 more compressible. 
 
 But ther^ are structures very soft and yielding in themselves, yet 
 enveloped 'in a rigid casing of bone which entirely shuts off the influ- 
 ence of external pressure. Hence the establishment of the equilib- 
 rium in them is wholly dependent upon an afflux of blood. This 
 gives us the third law, that structures w ithin closed bony cavities 
 are congested at the expense of all others. 
 
 In accordance with these laws, we shall find that while in the cais- 
 son, the condition of the different parts in regard to the supplj^ of 
 blood w ill be as follows : 
 
 The skin and the superficial structures will be antemic* The cen- 
 tral portion of the limbs and the interior organs of the body w ill be 
 congested. The solid viscera of the abdomen will be especially en- 
 gorged on account of both situation and structure. The brain and 
 spinal cord, and the interior of the shaft of the long bones, will be 
 congested to a high degree from the operation of the third law. 
 
 These changes are not perfected until a considerable time has been 
 passed in the compressed air. The circulation up to this point goes 
 on everywhere with vigor, the change being in the relative calibre of 
 
 * This is shown by the pallor which is very characteristic. See p. 21. 
 
32 
 
 the vessels, not in their tension. The counter-pressure becomes uni- 
 form throughout the \i hole vascular system, but this counter-pres- 
 sure supersedes the natural muscular resistance or tone of the vessels, 
 which have become passive tubes. The blood is distributed not in 
 accordance with the physiological demands of the different parts, but 
 in obedience to overpowering physical force. 
 
 This is the condition of the circulation at the moment that the pro- 
 cess of locking out begins. Yet the changes which have taken place 
 up to this point are not the cause of the morbid phenomena which 
 constitute the Caisson Disease, else the attack would take place while 
 in the compressed air, instead of after leaving it. It is evident that 
 the removal of the pressure, and not the pressure itself, is the immedi- 
 ate cause of the seizure. 
 
 This removal is effected in the few minutes which are occupied in 
 locking out. But it is not to be supposed that the vessels will in- 
 stantly assume their normal condition. They are in a state of relax- 
 ation, not only in the congested, but also in the anaemic parts ; in the 
 former, because of over-distension — in the latter, because the muscu- 
 lar coat cannot at once recover from its inaction. The aggregate 
 capacity of the vascular system will, therefore, be in excess, com- 
 pared to the volume of blood to be conveyed ; or, in other words, there 
 will be a lowering of vascular tension. 
 
 Hence, the circulation will be languid, and the congested parts w'U 
 not readily empty themselves of the excess of blood which they con- 
 tain. Especially will this be the case in the brain and spinal cord, 
 where the conditions are most favorable for the production of con- 
 gestion. The capillaries being clogged with eifete blood, the nutri- 
 tion of the part nmst suffer, and disturbance of function will result. 
 
 It is to this, I think, that the delirium, and the transient loss of 
 consciousness, which occasionally occur, are to be attributed. When 
 the spinal cord is the seat of this condition, pain in the parts deriving 
 their nerves from that section of the cord may result, or paralysis 
 more or less complete may follow. 
 
 This appears to me to account for the phenomena in those cases in 
 which the local symptom is paralysis or pain of a transient or shifting 
 character. These cases may, I think, be considered as entirely spinal 
 in their origin. But in many cases there are evident local changes 
 such as tumefaction, rise of temperature, etc., which indicate local 
 irritation, and which are probably due to obstruction of the vessels 
 of the part as a sequel to the local congestion. This explanation is 
 applicable also to those cases in which the pain is fixed in one locality, 
 which may be very much circumscribed, and where it persists for 
 days without intermission, feeling, as the patient expresses it, " as if 
 it were in the bone," where it very likely is. Such a pain presents a 
 
33 
 
 marked contrast to those shifting pains which have been described, 
 and if considered of spinal origin, would indicate a serious lesion con- 
 lined to a minute portion of the cord. That such a circumscribed 
 lesion might occur as a very rare exception, must be admitted ; but 
 that it should be present in a considerable proportion of cases is in 
 the last degree improbable. 
 
 The testimony of all observers is, that the liability to attack is di- 
 rectly as the duration of the stay in the caisson. This admits of an 
 easy explanation on the theory which I have advanced. The more 
 thoroughly the system has become adapted to the change in the 
 circulation, the less readily it will resume its normal condition when 
 the pressure is removed. The congested vessels, especially, will lose 
 their contractility in proportion to the time their muscular fibres have 
 been upon the stretch. 
 
 It was suggested by Francois, that the morbid phenomena result- 
 ing from high pressures might be due to the liberation of air which 
 had been absorbed by the blood while under pressure, but which was 
 set free again when the pressure was removed. 
 
 The same idea has since been advanced by Prof. Rameaux, of 
 Strasburg. 
 
 Within the past year M. Paul Bert has communicated to the 
 French Academy* the results of a series of experiments made upon 
 animals with very high pressui*es, reaching sometimes to 19 at- 
 mospheres. He shows that when death is the direct result of the pres- 
 sure it is induced by an excessive absorption of oxygen, which then 
 enters into chemical union Avith the blood, and acts as a poison. He 
 found that the gas w^hich escapes from the blood after the pressure is 
 removed, is composed of a mixture of nitrogen and carbonic acid, 
 with scarcely a trace of oxygen, the oxygen being retained by the 
 blood. This poisoning by oxygen, however, produces its effect while 
 in the compressed air, and therefore cannot be a factor in the pro- 
 duction of the Caisson Disease. 
 
 But M. Bert re-asserts the theory of Frangois and Prof. Rameaux, 
 with this difference : that he claims that bubbles of nitrogen instead of 
 air are the cause of the interruption of the circulation. These bub- 
 bles he has discovered after death in the vessels of the brain and 
 cord. But he states that Avhen the pressure does not exceed five 
 atmospheres, three minutes allowed for the restoration of the nor- 
 mal pressure will be found to prevent the formation of these 
 globules of nitrogen. Now, we find the Caisson Disease occurring 
 when the pressure does not exceed two atmospheres, and when six 
 to eight minutes are allowed for locking out. It Avould seem that 
 under these conditions, the gas should escape through the lungs as 
 
 * Comptes Rendu s, August, 1872, and February and March, 18T3. 
 
34 
 
 rapidly as it is disengaged from the blood. Moreover, we find that 
 in the Caisson Disease the attack often comes on several minutes or 
 even hours after leaving the compressed air. During this interval, if 
 any free nitrogen were circulating with the blood, it should constant- 
 ly become less by diffusion through the pulmonary membrane, and it 
 is scarcely conceivable that if the quantity at the moment of emerg- 
 ing into the open air were not enough to produce obstruction of the 
 circulation, such an effect could take place at a later period. 
 
 It is also very difficult to reconcile with M. Bert's theorj the fact 
 of the comparative immunity from danger which results from re- 
 peated exposures to the effects of compressed air. If the action be 
 that of purely physical causes, habit could make no difference. The 
 obstruction of the vessels described by Bert is a condition of which 
 the system could never become tolerant by frequency of repetition. 
 On the other hand, it is perfectly conceivable that vessels which are 
 required to receive a varying quantity of blood at different times 
 may acquire the power of more ready adaptation to these changes of 
 quantity, since this is only an extension of the physiological prin- 
 ciple which we see exemplified in all organs which have an intermit- 
 tent function. Hence this objection, which lies against the explana- 
 tion of M. Bert, does not api^ly to the views as to the pathology of 
 the disease which I have advanced. 
 
 Thus, while recognizing the value of M. Bert's observations, I am 
 still of the opinion that he is in error in applying them to the com- 
 paratively low pressures and gradual decompression which are con- 
 sistent with the production of the Caisson Disease. 
 
 In order further to test this question, I performed the following 
 experiment : The pressure in the caisson being about 35 lbs. to the 
 square inch, a dog was sent down, and allowed to remain seven hours 
 in the compressed air. At the end of that time I went down, and 
 after killing the animal with prussic acid, I opened the vessels of the 
 neck, and allowed four ounces of blood to flow into a six ounce vial. 
 The space above the blood was then completely filled with olive oil, 
 and a cork, pierced by one leg of a small U-shaped tube, was forced 
 tightly into the bottle, displacing a portion of oil, which escaped 
 through the tube. By this arrangement every particle of air was 
 excluded from the apparatus, even the tube, which extended a little 
 below the cork, being entirely filled with oil. The object of the oil 
 was to avoid the difficulty which would arise from coagulation of the 
 blood in the tube if blood only were employed. 
 
 The apparatus thus arranged was then taken into the open air. 
 While passing through the lock five minims of oil escaped from the 
 tube, which amount was increased during the next half iiour to eight 
 minims. The temperature of the caisson and that of the external 
 
35 
 
 air were almost exactly alike, so that the result obtained could not be 
 influenced by contraction or expansion due to temperature. The 
 eight minims, therefore, represented the bulk of air which was disen- 
 gaged from the blood in consequence of the removal of the excess of 
 pressure. This is only of the bulk of the blood experimented 
 upon. Now the experiments of Demarquay* show that from 80 to 
 150 c. centimetres of oxygen can be thrown into the veins of a me- 
 dium-sized dog in the space of four or five minutes, without pro- 
 ducing serious consequences ; and other observers have demonstrated 
 that air slowly introduced into the veins escapes through the lungs, 
 and that a large quantity can be injected in this way without danger. 
 
 Hence with the small amount of air which my experiment shows 
 to be disengaged from the blood, and with the process extended over 
 eight or ten minutes at least, it seems clear that we cannot explain in 
 this way the phenomena observed in the Caisson Disease. 
 
 Causes. — The one essential cause, without which the disease can 
 never be developed, is the transition to the normal atmospheric pres- 
 sure, after a prolonged sojourn in a highly condensed atmosphere. Hence 
 we have to consider two elements, pressure and time. As the mo- 
 mentum of a moving body is found by multiplying the weight by the 
 velocity, so the danger in these cases is as the degree of pressure to 
 which the person has been exposed, multiplied by the duration of the 
 exposure. 
 
 But inasmuch as a prolonged sojourn in the caisson does not in 
 every case produce the disease (many of the men employed escaping 
 it entirely), \% follows that there must be concurrent causes which de- 
 termine its development. This is what we observe in many other 
 diseases of a specific origin. Thus the essential cause of intermit- 
 tent fever is exposure to a peculiar malaria, yet only a portion of 
 those so exposed are affected by the disease. 
 
 The first of the concurrent causes of the Caisson Disease is a 
 special predisposition. This is occasionally strongly marked, some 
 persons being affected by a short exposure to a low pressure from 
 which there would generally be experienced no inconvenience what- 
 ever. 
 
 Tlie study of these cases has led me to the suspicion that they 
 afford a key to the singular, though very common, predisposition to 
 pams in the limbs on the approach of a storm. . These pains are gen- 
 erally considered to be of a rheumatic character, and to depend upon 
 the dampness of the atmosphere. But inasmuch as the disease we 
 are considering affords examples of pains precisely the same in char- 
 acter, but immensely intensified in degree, resulting from the diminu- 
 tion of an atmospheric pressure to which the system had adapted it- 
 * Pneumatologie MecUcale. P. 664. 
 
36 
 
 self, and irrespective of any question of humidity, analogy suggests 
 that the so-called rheumatic cases are simply exaggerations of a pre- 
 disposition, identical in kind with the one under discussion, and are 
 produced by the low barometric condition of the atmosphere which 
 precedes a storm, and not by the influence of moisture. It is true 
 that the change in the pressure is insignificant when compared with 
 that which produces the Caisson Disease, but it is supplemented by the 
 immensely greater dm-ation of the higher pressure to which the sub- 
 ject has been previously exposed. Persons suffering in the manner 
 referred to, regard themselves as walking hygrometers, and are ac- 
 customed to say, ' ' I feel the dampness in my bones. " I would sug- 
 gest that they are rather barometers, perhaps quite as sensitive as 
 the instrument of Torricelli. 
 
 Perhaps the most frequent exciting cause of the Caisson Disease is 
 too rapid locking out. Indeed, it is altogether probable that if suffi- 
 cient time w^ere allowed for passing through the lock, the disease 
 would never occur. But w^hat is sufl[icient time for one is too short a 
 time for another, and as no work could be accomplished if the time 
 in the lock were indefinitely prolonged, all that can be done is to fix 
 upon a duration for the process of locking out which shall be propor- 
 tioned to the pressure, and as great as is consistent with the circum- 
 stances, and then to see that the rule is rigidly observed. The natu- 
 ral impatience of the men to reach their homes, makes the dela}^ in 
 the lock irksome, and great firmness is required on the part of the 
 lock-tender to prevent the escape-cocks being opened more widely 
 than is consistent with safety. In locking out, at least five minutes 
 should always be allowed for each additional atmosphere of pressure. 
 
 Neimess to the Work. — Unquestionably the liability to the Caisson 
 Disease is greatest in those exposed for the first time to the influence 
 of the compressed air. New hands are very apt indeed to suffer more 
 or less during the first week, and a number of the severest cases that 
 came to my nptice, occurred in men who had worked but a single 
 watch, though first attacks were much more likely to occur after the 
 second watch of the first day. Those least affected were such as 
 began work when the pressure was comparatively slight, and contin- 
 ued without intermission as the pressure increased. It seemed that 
 the system after a time became adapted to the changed conditions, 
 and was protected, in a measure, from their effects. Nevertheless, 
 some serious cases occurred among the old hands, especially when for 
 any reason their stay in the caisson was prolonged beyond the usual 
 time, thus showing that their immunity was merely relative. A 
 sudden increase of pressure, also, even though very slight, was cer- 
 tain to develop new cases— men thoroughly inured to the work 
 often being affected under such ckcumstances. 
 
37 
 
 Fullness of Habit. — After the work in the Xew York caisson had 
 been some months in progi'ess it was observed that there w^as a pre- 
 ponderance of stout, heavily-built men among those taken sick. 
 This led me to examine my records carefully in reference to this 
 point. I found that up to May 22, the}^ embraced 86 cases of well- 
 marked Caisson Disease. These I di\ided into three classes, accord- 
 ing to the build of the individual. Those who were tall in propor- 
 tion to then- weight, and rather lean in flesh, were classed as spare ; 
 those who were thick-set and muscular, without being fat, were set 
 down as medium ; and those with prominent abdomen, full cheeks, 
 and general tendency to obesity, were stj'led Jieavy. The 86 cases of 
 illness were found to be distributed among these three classes as fol- 
 lows : Spare, 28 ; medium, 22 ; heavy, 36. 
 
 Considering that among laborers below the age of 45 (and none of 
 the cases were above that age), the class described as heavy are very 
 much in the minority, these figures were suificiently striking. 
 
 In order to arrive at the converse of this I desired the time-clerk 
 to prepare a list of those who had lost least time from illness, i.e., 
 those least affected by the work. The figures in this case were even 
 more striking. The list comprised the names of 42 men, who were 
 classified as follows : Spare, 25 ; medium, 14 ; heavy, 3. 
 
 I next separated the severer cases of illness, which were marked 
 by parah^sis ; of these there were 13 : Spare, 2 ; medium, 3 ; heavy, 
 8. Those who had died up that time, three in number, were alllieavy 
 men. 
 
 These results may be tabulated as follows : 
 
 
 Spare. 
 
 Medium. 
 
 Heavy. 
 
 Total. 
 
 Lost little or no time from sickness. . . 
 
 25 
 
 14 
 
 3 
 
 42 
 
 
 28 
 
 22 
 
 36 
 
 86 
 
 Paralyzed 
 
 2 
 
 3 
 
 8 
 
 13 
 
 Died 
 
 
 
 8 
 
 3 
 
 These figm-es show unmistakably that a tendency to fullness of 
 habit renders work in a compressed atmosphere much more hazard- 
 ous. Persons of this build have more fluids in the body, the distribu- 
 tion of which is changed by the pressure, in the manner before 
 stated, and it is therefore not suiprisiug that the effect upon them 
 should be greater than upon lean and siuewj- persons, whose bodies 
 contain a minimum of fluid. 
 
 Severe Exertion Immediately after Leaving the Caisson. — As at the 
 moment of going out of the compressed air the system undergoes a 
 
38 
 
 violent reaction, it is manifestly unfitted to bear in addition a severe 
 tax upon the muscular strength. Hence, the ascent of a long flight 
 of stairs, immediately after leaving the air-lock, is as wrong in theory 
 as it has proved bad in practice Dr. Jaminet has described most 
 graphically the ill eifects arising from this cause at St. Louis, and 
 the relief experienced when the men were saved the necessity of 
 climbing the steps by the substitution of a steam elevator.* Con- 
 trast this with the experience of M. Triger, whose apparatus at Cha- 
 hmnes was so arranged that the ascent of the ladder took place in 
 the compressed ah-, the lock being placed at the top instead of the 
 bottom of the shaft. He found that the men ascended a distance of 
 70 feet without becoming in the least out of breath ; making the 
 ascent, in fact, much more easily than if it had been in the open air. 
 
 I hoped at one time that an opportunity would be afforded at the 
 New York caisson for obtaining some data bearing upon this point. 
 During the early part of May an elevator was arranged, but unfortu- 
 nately just at that period great changes took place in the force, and 
 at the same time various interruptions in the work occurred, so that 
 the matter was hopelessly complicated, and no data for comparison 
 could be obtained. 
 
 Tlie Abuse of Alcohol. — Sev^aral writers have remarked that habit- 
 ual drinkers are more likely to be affected by compressed air than 
 those who used spirits moderately or not at all. It is stated by the 
 director of the work at Douchyf that the attacks from which the 
 men suffered were " almost always coincident with some excess com- 
 mitted in the interval of the shifts." It is easy to perceive that as 
 the disease is characterized by cerebral congestion, the abuse of alco- 
 hol, which has a tendency to produce the same result, would act as a 
 predisposing cause. Although no cases directly attributable to this 
 cause came under my observation, I have no doubt that there is 
 danger from it; and I therefore rejected several men who applied for 
 work in the caisson, for no other reason than that their appearance 
 indicated an habitual excessive use of alcohol. 
 
 Entering the Caisson Fasting. — Dr. Jaminet insists very strongly 
 upon the influence of this cause, and cites instances to prove his 
 position. Several cases corroborative of his views occurred under 
 my observation. One of the rules for the men working in the New 
 York caisson, prohibited entering the compressed air without having 
 taken food, and in addition to this each new hand was especially 
 cautioned as to the danger of disregarding this precaution, and the 
 foremen were directed to use every effort to secure its observance. 
 Yet notwithstanding all this a number of very severe attacks were 
 
 *See Dr. J.'s Report, p. 120. 
 
 t Annales d'Hyg. Pub. et de Med. Legale, 1854. 
 
39 
 
 foimd to b3 coincident witli, if not dependent upon, violations of this 
 rule. In these cases epigastric pain and retching were prominent 
 symptoms. (See Case XXI., p. 47.) 
 
 Treatment. — The treatment of this disease will depend upon the 
 severity of the case, and the presence or absence of gastric symp- 
 toms or of paralysis If we have to deal with the neuralgic pains 
 only, the chief reliance must be upon anodynes, administered with a 
 liberal hand. Fortunately the pain, though very severe while it 
 lasts, is in most cases of short duration, the attack passing off 
 usually in a few hours. 
 
 It is, therefore, quite practicable to keep the patient under the 
 influence of morphine during the whole time, and thus enable him to 
 escape entirely all extreme suffering. But large doses will be 
 required, the intense pain inducing a remarkable tolerance of the 
 drug. It was my habit to give half a grain of morphine at the 
 outset, and a quarter of a grain every half hour afterward until 
 relief was obtained. When emplo^'ed hypodermically, which is the 
 method affording most prompt relief, somewhat smaller do^cs may 
 be used. 
 
 In some instances I have obtained the very best results from hypo- 
 dermic injections of atropine at the seat of pain ; but in other cases 
 it failed to procure relief, and, upon the whole, I consider it inferior 
 to morphine. 
 
 Dr. Jaminet, regarding the affection as wholly the result of 
 exhaustion, relies entirely upon stimulants and concentrated nourish- 
 ment, ignoring the aid of anodjnies altogether. I can see no reason 
 for this, even admitting to the fullest extent his theory of the dis- 
 ease, for nothing can be more exhausting than the intolerable pain 
 which characterizes this affection, and nothing could act more 
 promptly as a restorative than an efficient anodyne. 
 
 Starting from the theory already given as to the mode in which 
 the disease is produced (a theory which was constructed wholly upon 
 the observations of others), I was led to the idea that benefit would 
 be derived from the use of an agent that would induce contraction of 
 the capillaries, and thus correct the want of tone which I considered 
 to lie at the foundation of the difficult3\ For this purpose I pro- 
 posed the use of ergot before I had ever seen a case of the dis- 
 ease. I reasoned that it would be useful, first, by contracting the ves- 
 sels of the brain and spinal cord, and relieving their congested state : 
 and secondly, by restoring tone to the superficial vessels, and thus 
 imparting vigor to the circulation. 
 
 An extended trial warrants me in sajing that the results have jus- 
 tified the theory. In my hands, though not always successful, ergot 
 has certainly been very useful in a considerable number of cases. 
 
40 
 
 I have seen very severe pain completely relieved within half an hour 
 after the administration of a di*achm of the fluid extract. In other 
 instances, unsteadiness of the limbs, which seemed about to usher in 
 paralysis, has yielded promptly to one or two doses. 
 
 But perhaps the best evidence of its usefulness is to be found in 
 the preference for it of the night-porter, who had charge of the hos- 
 pital at night, and who was instructed in the use of the few medi- 
 cines employed, and treated such cases as occurred among the men 
 composing the night gangs. Having both morphine and ergot at 
 hand, he gradually, and of his own accord, almost abandoned the 
 former, declaring that the ergot was more prompt and certain in 
 relieving the pains. This from an intelligent, unprejudiced, non- 
 professional source, is strong testimony in favor of the eflSciency of 
 the drug. 
 
 I was in the habit of giving a teaspoonful of Squibbs' fluid extract, 
 and repeating the dose in half or three-quarters of an hour, unless 
 the pain was relieved. In one case ergotine was injected hypoder- 
 mically ; but so much irritation was caused at the point of insertion 
 that the experiment was not repeated. 
 
 Frictions, with or without stimulating liniments, are very generall}' 
 resorted to, and seem sometimes to give momentary relief, but it ap- 
 pears to me to be rather by occupying the attention of the patient 
 than by any action occasioned in the part. 
 
 In one of my cases of pain in the knee, compression of the femo- 
 ral artery with the fingers w^as tried. The pain was considerably re- 
 lieved for a few minutes, but soon acquired its former severity. In 
 another case a tourniquet was applied so as to interrupt the venous 
 as well as the arterial circulation, but with no better result. 
 
 In some instances where the pain was confined to a particular lo- 
 cality, I had the part immersed in hot water, with the effect of caus- 
 ing temporary relief. But the use of the general hot bath was not 
 advised, as I considered it unsafe to increase the already existing re- 
 laxation of the vessels. In several of Dr. Jaminet's cases paralysis 
 came on while in the hot bath, and he therefore interdicted its use. 
 
 Toward the last of my experience I applied cold to the spine in 
 two cases, with apparent benefit in each. In one of these cases, in 
 which there was paralysis of the bladder, the improvement after a 
 cold douche to the spine was marked. 
 
 In one case of paraplegia, dry cups applied to the spine in the lum- 
 bar region were unmistakably beneficial. 
 
 Electricity was tried by Dr. Jaminet at St. Louis, but was found 
 to be useless. 
 
 Epigastric pain is almost always relieved at once by the use of an 
 alcoholic stimulant with ginger, as employed by Dr. Jaminet. 
 
41 
 
 Vomiting is best treated with sinapisms to the epigastrium, and 
 swallowing small bits of ice. A full dose of calomel was effectual 
 in one of my cases which resisted all other treatment. 
 
 When paralysis occurs, it is to be treated on general principles. 
 Cups or leeches, with douches and frictions to the spine, may be use- 
 ful ; and if the case be protracted, the use of strjxhnine may be called 
 for. The bladder will almost certainly be involved, requiring the 
 constant employment of the catheter. 
 
 The cerebral symptoms which occasionally occur, are, Avith the ex- 
 ception of coma, so transient in their natm*e as to call for no special 
 treatment. Coma, when it takes place, is to be managed according to 
 the circumstances of the case, as when proceeding from other causes. 
 If accompanied by a full, strong puLse, venesection may be expe- 
 dient. 
 
 There remains to be considered a plan of treatment originally sug- 
 gested by Pol, and carried out to some extent by Foley, viz. , return- 
 ing the patient at once into the compressed air. 
 
 It frequentl}' happened under ni}^ observation, that pains not suffi- 
 ciently severe to deter the men from retm^ning to work, were promptly 
 dissipated on entering the caisson, to retm-n again on coming into the 
 open air. Indeed, I do not remember a single exception to the rule, 
 that any pain which may have been felt before, disappeared almost 
 imme<:liately on going below. 
 
 Foley says, as the result of his experience : "A true specific is re- 
 tm*ning to the caisson, thi'ough which means all such accidents (pains, 
 vertigo, etc^f) speedily disappear. It is to be resorted to unhesitat- 
 ingly in all thi-eatening cases, and the pressure should be admitted 
 rapidly." 
 
 But the means of access to the caisson are usually such that it 
 would be difficult to remove a patient into it, even if he could be 
 comfortably cared for while there, or if his presence would not in- 
 terfere with the work. It would, therefore, be desu*able to have 
 facilities for employing compressed air at some point above ground 
 which would be easily accessible. 
 
 My plan would be as follows : Let them be constructed of iron of 
 sufficient thickness, a tube 9 feet long and 3^ feet in diameter, having 
 one end permanently closed, and the other provided with a door open- 
 ing inward, and closing air-tight. This tube to be placed horizon- 
 tally, and provided with ways upon which a bed could be slid into it. 
 Ver}' strong plates of glass set in the door and in the opposite end 
 would admit the light of candles or gas jets placed immediately out- 
 side. This apparatus should be connected by means of a suitable tube 
 with the pipe which conveys the air from the condensers to the 
 caisson? An escape-cock properl^^ regulated would allow the constant 
 
42 
 
 escape of sufficient air to preserve the necessary purity of the at- 
 mosphere within. 
 
 The bed containing the patient having been slid into the chamber, 
 the door is to be closed, and the pressure admitted gradually until it 
 nearly or quite equals that in the caisson. This should be continued 
 until the patient indicates by a signal previously concerted, that the 
 pain is relieved. The pressure should then be reduced by degrees, 
 carefully adjusted to the effect produced, until at last the normal 
 standard is reached. By occupying several hours, if necessary, in the 
 reduction of the pressm*e, it is probable that a return of the pain 
 could be avoided. 
 
 The apparatus once provided, there would be no difficulty in car- 
 rying out the plan in any case of such severity as to resist other 
 treatment. I should expect the very best results from it in cases of 
 extreme pain, or in the very outset of paralysis not dependent upon 
 extravasation of blood. 
 
 Of course the secondary conditions which arise in protracted cases 
 would not be capable of direct relief by simply reproducing the phys- 
 ical conditions existing in the caisson. The most that might be 
 hoped for in such cases would be that the pressure might result in 
 giving a new impulse to the circulation in the congested part, and 
 thus favor resolution. 
 
 Reasoning from his view of the pathology of the disease, M. Bert 
 has proposed the inhalation of oxygen, in order to displace the free 
 nitrogen from the blood by diffusion. Experiments upon animals 
 demonstrated that the sounds produced in the heart by the presence 
 of free nitrogen, speedily disappeared when the animal was made to 
 inhale oxygen, the nitrogen diffusing into this gas much more readily 
 than into common air. But though immediate death was averted by 
 this expedient, paralysis nevertheless occurred, and post mortem 
 examination showed the presence of bubbles of nitrogen in the 
 vessels of the cord. 
 
 A tendency to pulmonary congestion seems to be induced by high 
 atmospheric pressure in certain rare instances. Such cases are men- 
 tioned by Frangois and Jaminet, and two instances came under my own 
 observation, one of which was almost instantly fatal. (Case XXX.) 
 
 The mechanism by which these congestions are produced is not 
 apparent. If in every instance they occurred immediately upon 
 passing from the caisson into the open air, it might be inferred that 
 the expansion of the air contained within the lung produced, in some 
 way, an interference vnth the pulmonary circulation. But inas- 
 much as a rapidly fatal congestion may come on an hour or more 
 after leaving the caisson, this explanation is not sufficient. The 
 
43 
 
 subject is involved in obscurity, which can be removed only by the 
 study of a larger number of cases than have occurred as yet. 
 
 CHAPTER SIXTH. 
 
 ILLUSTRATIVE CASES. 
 
 The following cases have been selected from my notes as illustrat- 
 ing the various affections resulting fi-om compressed air which have 
 been described in the foregoing text. Also, a few cases, as will be 
 seen, have been borrowed from other sources. 
 
 Case I. — John Campbell, lock-tender, on the 11th of February, was 
 "caught in the lock, " ^. e., found himself unable to equalize the 
 pressure in the left ear. The pain, however, not being severe, he 
 completed his day's w^ork. The following night was taken with 
 very severe pain in the ear, which continued without intermission 
 until the 20th, when a profuse discharge of pus fi-om the external 
 ear set in, affording relief from the pain. Under the use of carbolic 
 acid injections the discharge soon ceased, leaving the hearing unim- 
 paired. 
 
 Case 11. — John Hicks. Taken on the 17th of May, while in the 
 lock going down, with severe pain in the right ear, followed by a 
 slight discharge from the external meatus. No sensation as of any- 
 thing giving way in the ear. He completed his watch and then 
 reported to me. On examination, the drum of the eai' was found to 
 be rupturec? at its upper edge. The opening was nea^'ly circular, and 
 rather less than a line in diameter. The patient preferred to give up 
 his place at once, and did not report again. Though he stated that 
 he had had no previous trouble with the ear, the fact of the discharge 
 when the membrane was ruptured, leads to the suspicion that there 
 was catarrh of the middle ear, which probably accounted also for the 
 stoppage of the Eustachian tube. 
 
 Case III. — (Francois).* Patient at Argenteuil seized with otalgia 
 on coming out of the caisson, where the pressure was 13 lbs. to the 
 inch. Pain persisted for 15 days without intermission, notwithstand- 
 ing the most active treatment, including pm-gatives and the applica- 
 tion of leeches and antimony behind the ear. Condition of the 
 tube or of the di*um not stated. 
 
 Case IV. — Patrick O'Farrell. Reports March 11th, that he was 
 taken four days ago, on going down into the caisson, with pain in 
 the region of the fi-ontal sinus. On coming up, the pain was in- 
 creased, and there was bleeding from the nose. The pain has con- 
 tinued ever since. Ordered anodynes and hot fomentations. 
 
 * Annales cl'Hygiene Publique, et de Med. Leg. T. XIV. i860. 
 
44 
 
 14th. Reports for duty. 
 
 Case V. — Hugh Rourke. March 12th, while gomg home in the 
 evening, was taken with severe pain in the right knee. Pain continued 
 all night. On the following morning he returned to his work, when, 
 on entering the caisson, he found that the pain ceased at once. On 
 coming up again it returned with increased severity. Controlled by 
 morphine. 
 
 Case VL — John Roland. Taken on March 8ch, while in a car 
 going home. Dizziness and loss of strength ; feet cold, head hot ; 
 unable to stand, but still not paralyzed — simply weak. No pain. 
 Profuse cold perspu-ation. Recovered perfeetl}" in a few hours with- 
 out treatment. 
 
 Case VII. — Alfred Symes. Suffered somewhat with pain in the 
 right knee, on coming up from the caisson on the 10th of May. On 
 the 11th he worked as iisual, experiencing no pain. On the 12th 
 (Sunday), not having been in the caisson since the day previous, he 
 was taken with severe pain in the same knee. When he reported to 
 me, on the 14th, he was suffering with a swelling of the knee, ac- 
 companied by heat and extreme tenderness, especially just above the 
 patella. He was ordered to apply fomentations, with a hot solution 
 of bicarbonate of potash. Under this treatment the pain and swell- 
 ing soon subsided. On the 15th, there was a greenish yellow tinge 
 of ecch3^mosis over the front of the knee, for a space as large as the 
 palm of the hand. 
 
 Case YHI.— Samuel Mitchell. Worked for one watch only on the 
 14th of May, being his first experience in compressed au\ After the 
 first watch, on the 15th, he was taken with pain in both the upper 
 and lower extremities, and also in the chest and bowels. This was 
 followed by giddiness and vomiting. There was paralysis of the left 
 leg and weal^Jiess of the right arm. Profuse sweating. Pulse 80. 
 Ergot and chloral given. Paral3'sis passed off in two hours, leaving 
 slight pain in the ai'ms and wrists. The bowels had not been opened 
 for several days. 
 
 Case IX.— John Kennedy. This patient had engorgement of the 
 left mammary gland, recurring each day after coming out of the 
 caisson, and especially after the second watch. There was marked 
 swelling and tenderness, which disappeared during the afternoon and 
 evening, to recui- again on the following day. This continued for 
 more than a week. 
 
 Case X. — Joseph Hatch. Taken sick on the 17th of May, after 
 his first watch. Epigastric pain and pain in the legs and arms, fol- 
 lowed by paraplegia. Treated with ergot only. At the end of four 
 hours he had recovered the use of his limbs, and the pain had ceased, 
 but there remained a giddiness which prevented his standing. By 
 
45 
 
 the following clay lie was able to walk about, but the giddiness had 
 not entirely disappeared when I last saw him, May 21st. 
 
 Case XI. — E. Riley. Taken sick Feb. 16th, one hour after leaving 
 the caisson. Pressure 26 lbs. Epigastric pain and pain in the legs. 
 No loss of sensibility. Profuse cold perspiration. Pulse, when I saw^ 
 him, two hours after the commencement of the attack, was 96. The 
 pain, which at first w^as veiy severe, had hy this time become much less. 
 Gave him an ounce of brandy and a teaspoonf ul of fluid extract of 
 ergot. In 10 minutes the pulse had fallen to 82. Was able to resume 
 work next day. 
 
 Case XII. — Joseph Brown, foreman, American, aged about 28. 
 Taken on the 28th of February, about an hour after coming up from 
 a three hours' w'atch. Excessive pain in left shoulder and arm, com- 
 ing on suddenly, "like the thrust of a knife." Pain continued uatil 
 he went down again for the afternoon watch, when it ceased imme- 
 diately. On the following morning there was a spot on the shoulder 
 and one on the arm, at the points where the pain had been most 
 severe, where the skin was speckled with minute bright red points of 
 extravasated blood. Had had no pain since the day before, but the 
 parts were tender to the touch, with at the same time a feeling of 
 numbness. 
 
 Case XIII. — Henry Stroud, a diver by occupation, began work on 
 the morning of April 2d. Half an hour after coming up from the 
 first watch, was taken with numbness and loss of power in the 
 right side, also dizziness and vomiting. This was followed by severe 
 pain over t^e whole body. Excessive perspiration. Was treated 
 with stimulants and ergot, and in five hours was well enough to re- 
 turn home. 
 
 Case XIV.— John Barnabo, Italy, 43, reports that on the 13th of 
 March, while in a car returning home, he was taken with severe pain 
 in both arms. This was followed by dimness of sight and partial 
 unconsciousness. Extremities very cold. Remained in this condi- 
 tion for tw^o hours. Was obliged to keep his bed for three days. 
 For a week afterward was unable to work, feeling very much op- 
 pressed about the chest. Had no medical attendance. Had a simi- 
 lar but less severe attack about a month previously. 
 
 Case XV. — J. Avers. Taken on the 7tli of April with very severe 
 pain in both knees, coming on within a few minutes after leaving the 
 caisson. A drachm of the extract of ergot was given every hour for 
 three hours, then two more doses at intervals of two hours, after 
 which he was completely relieved. 
 
 Case XVI. — Frank Murphy. Taken sick April 8th, after the sec- 
 ond watch of his first day in the caisson. Extremely severe pains in 
 both knees and in the right shoulder ; -^^ of a grain of atropine was 
 
46 
 
 injected beneath, the skin of the shoulder, but aiforded no relief. 
 Half a grain of morphia by the mouth, did not check the pain. Legs 
 placed in hot water, which gave immediate relief. Ergot was also 
 given in drachm doses hourly. Returned home much better, but the 
 pain subsequently returned, and was very severe at times for several 
 days. 
 
 Case XVII. — Charles Peterson. Taken on the 11th of April with 
 severe pain in both legs and in the right arm. Was relieved by ergot, 
 but had severe pain each day afterward on coming up. On the 15th 
 he was ordered a teaspoonful of the fluid extract of ergot, fom- times 
 a day, after which there was no further complaint. 
 
 Case XVIII. — Card, foreman. Taken on the 17th of April, after 
 the first watch, with quivering in the thighs, followed by loss of 
 power in the lower extremities, and anasthesia. There was 
 also partial paralysis of the bladder. These symptoms con- 
 tinued until the 19th, when they disappeared, leaving great sore- 
 ness of the muscles of the calves. After the paralysis had passed off 
 in a measure, he went down again into the caisson and remained for 
 a short time with decided benefit, The improvement continued after 
 returning to the open air. He had no other medication than two 
 doses of ergot. 
 
 Case XIX. — James HefCener. Attacked May 2d, ^oon after leav- 
 ing the caisson, with pain in the limbs and in the epigastrium, fol- 
 lowed by vomiting of large pieces of undigested meat. Eyes swollen 
 and very much injected; extreme giddiness; pulse 80, and small. 
 Vomiting continued at intervals for 24 hours. Bowels had not been 
 moved for 48 hours. 
 
 Was treated with morphia and ergot, but the vomiting continuing, 
 a scruple of calomel was given on the 3d, which had the effect of 
 quieting the stomach, and at the same time of relieving the bowels, 
 after which the patient quickly recovered. 
 
 Case XX. — Thos. Kirby. Taken April 30, with severe pain in 
 the right forearm. The patient was seen by Dr. G M. Beard, at 
 whose suggestion I injected into the middle of the palmar aspect of 
 the forearm two minims of a solution of ergotine, each minim con- 
 taining a grain of the drug. The following day, considerable swell- 
 ing had taken place at the point of puncture. The original pain still 
 continued, though less severe. On the 4th day of May, the patient 
 presented himself with a similar, though more extensive, swelling on 
 the other side of the arm, the previous swelling having disappeared. 
 This secondary swelling followed very closely upon the first. It sub- 
 sided promptly under the use of cold applications ; but on the 10th, 
 another similar swelling appeared on the part of the arm above the 
 elbow. It was excessively hot and painful. By the continuous use 
 
47 
 
 of ice, it was soon dissipated witlioiit suppuration. The patient did 
 not enter the caisson from the time of the first attack until his final 
 recovery. 
 
 Case XXI. — Brune Wieland, Germany, aged 23. Attacked on the 
 8th of ]May, after working two hoiu's in the caisson, Avhich he entered 
 for the first time, and without having taken food. The attack began 
 •with pain in the epigastrium, and vomiting soon followed by para- 
 plegia, and gi-eat depression. Respiration 40, pulse 100, and very 
 feeble. Stimulants brought about a prompt reaction. The power of 
 motion was soon regained, but there was not sufficient strength in the 
 legs to stand. Paralysis of the bladder. On the following day he was 
 perfectly comfortable, though still too Aveak to stand. Bladder still 
 paralyzed. Sent to the hospital, after which there is no record of his 
 case. 
 
 Case XXII. — Patrick Rogers, Ireland, aged 40, reported at my 
 office at the pier that the day previous he was taken while on the 
 ferry-boat going home, with pain in the right side, soon followed by 
 loss of feeling and power to move or stand. This was about thi-ee- 
 quarters of an hour after leading the caisson, where the pressure was 
 26 lbs. to the inch. On the arrival of the boat he was placed in a 
 hack, and taken honie. According to his account, he was for four 
 hours completeh' paralyzed in the legs, and partly so in the arms. A 
 physician was called, who gave a medicine which caused vomiting, 
 after which there was profuse cold perspiration. Sjniiptoms grad- 
 ually passed off, and by 3 P. M. of the following day he was well, 
 with the exception of weakness and a nimib feeling of the skin. A 
 drachm of fhe fluid extract of ergot was ordered to be given every 
 hoiu- until four doses had been taken. On the 17th, he reported him- 
 self as much better. Soon after taking the first dose of ergot, he 
 found his strength improved. He now felt well, except a " trembling " 
 in the chest. Advised not to resume work in the caisson. 
 
 Case XXIII. — Charles Ward. Began work May 17th, and con- 
 tinued through both watches, though advised to omit the afternoon 
 watch for the first day or two. After coming up the second time, he 
 felt some pain in the legs. Did not work again until the 20th, when, 
 after the first watch, he was taken with numbness in the left leg, 
 and partial loss of motion. When I saw him on the 21st, the sensi- 
 bility in the affected part was yeiy much blunted, but the power of 
 motion was fully restored. Temperatm'e to the hand sensibly lower 
 than in the other leg. Xo pain. Complaint of a ''Avant of hold 
 upon the ground " in attempting to walk. 
 
 Cold water was poured upon the lower part of the spine for several 
 minutes, after which there was a decided improvement in the leg. 
 He was able to walk home ; but did not report again, and I lost sight 
 of the case. 
 
48 
 
 Case XXIV.— Fred. Wilkinson. Taken May 21st, after the second 
 watch, with pain in the right knee. Considerable swelling above 
 and internal to the patella. Slight elevation of temperature. Re- 
 lieved by the cold douche. 
 
 The minutes of the following case were kindly furnished me by 
 Dr. Walter Reed, of the Brooklyn City Hospital, and are so interest- 
 ing that I transcribe them in full : 
 
 Case XXV. — "Michael Madigan, age 36, Ireland, laborer, admitted 
 March 26th, 1872. A large, robust man ; states that he has been 
 working on the East River Bridge for three months past, and that 
 for several weeks x)ast has been under a heavy atmospheric pressure 
 (about 30 lbs.) 
 
 "March 25th, about noon, after coming up from the caisson, was 
 taken with cramps in his stomach, which required a dose of medi- 
 cine for their relief. He then went to his dinner, after which he re- 
 turned to work, but felt so weak in the legs and in the small of the 
 back that he was compelled to leave off. Was carried home and put 
 to bed. Did not have much pain in the legs or back, but a feeling of 
 extreme weakness. Slept but little during the night, and in the 
 morning found that his legs were powerless, nor could he pass his 
 water, which had to be duawn with a catheter. On admission there 
 was found to be paralysis of the legs, with slight diminution of 
 sensibility. No pain in limbs. Slight tenderness on pressure over 
 the lumbar vertebrae. Paralysis of bladder. Urine drawn off ; 
 quantity, 8 oz. Acid reaction : no albumen. Dry cups applied to the 
 lower part of the spine. Ordered liq. amnion., acetatis, to be re- 
 peated in an hour. At bed time potas. bromid. grs. 40. 
 
 "March 27th. Find patient improved. Slept well during the night. 
 Took some breakfast. Can move his right leg to a considerable ex- 
 tent ; left leg powerless. Has slight pain in the back. Urine drawn 
 off, 8 ozs. ; acid. P. M. , to re-apply dry cups to spine. 
 
 "March 28th. Can move both legs very well. Is able to stand, but 
 his knees soon bend under him. Urine drawn off. Cups re-applied. 
 
 ' ' March 29tli. Can stand up and walk a few steps, though this re- 
 quires some exertion. Cups again to the spine. Urine drawn off. 
 
 " March 31st. Still improves ; walked to the water-closet and had a 
 movement of the bowels. This is the second movement since admis- 
 sion. The first was an involuntary evacuation in the bed. 
 
 " April 2d. The patient has regained the power over his bladder, 
 and passes his urine twice a day. Feels much stronger. 
 
 "April 5th. Patient has been walking about the yard. Says he 
 feels well, except a slight weakness in his back. Discharged cured." 
 
 For some time after his discharge from the hospital, this patient re- 
 mained very feeble, and the catheter was occasionally required to re- 
 
49 
 
 lievc the bladder. He was confident that he received great benefit 
 from the dry cups while in the hospital, feeling better each time as 
 soon as they were applied. In this statement Dr. Reed concuiTed. 
 
 Case XXVI. — Reardon, England, 38, corpulent, began work on 
 the morning of May 17th ; was advised to work only one watch the 
 first day, but, nevertheless, feeling perfectly well after the first 
 watch, went down again in the afternoon. The pressure at this time 
 was about 35 lbs. , the duration of the morning shift 2^ hours, that 
 of the afternoon shift 2 hours. Immediately after coming up from 
 the second watch Reardon was taken with very severe pain in the 
 stomach, followed by vomiting. In a few minutes the pain seized 
 upon the legs, which soon lost the power of motion, though they con- 
 tinued to be the seat of extreme pain, and were not entirely insensi- 
 ble to pinching or pricking. The vomiting continued all night, and 
 toward morning he Avas removed to the Centre street Hospital, where 
 he gradually sank, and on the 18th died. 
 
 The autopsy showed a slight engorgement of the lungs. All the 
 other thoracic and abdominal viscera, as well as the brain, were 
 healthy. The spinal cord was found to be intensely congested, and 
 opposite the two lower dorsal vertebra?, there Avas an extensive effu- 
 sion of blood pressing upon the cord. 
 
 Case XXVII. — Patrick McKay, Ireland, 50. Had been four months 
 at Avork in the caisson, and had not complained of ill-health. On the 
 30th of April he remained in the caisson half an hour beyond the 
 usual time, at the second watch, the pressure being about 34 lbs. 
 Some other persons who were Avitli him in the lock, AA'hen about leav- 
 ing, found that he was sitting with his back against the Avail of the 
 lock, quite insensible. He was at once carried up to the surface, and 
 removed to the Park Hospital, Avhere I saw him shortly afterwards. 
 He Avas there in an unconscious condition ; face pale and dusky ; lips 
 blue ; pulse irregular and feeble. Under the administration of stimu- 
 lants, he recovered some degree of consciousness, and begged inces- 
 santly for water. The urine As^as draAA^n with a catheter, and found 
 to be intensely albuminous. Paroxysms of convulsions soon set in, 
 in one of Avhich he died, nine hours after the attack. 
 
 The autopsy, at AA^hich I Avas not present, showed that all the 
 organs Av^ere healthy, except the kidneys, Avhich Avere the seat of 
 Bright's disease, and were very much altered in structure. 
 
 In this case the effect of the compressed air was merely to hasten 
 an event which, at best, could not have been very long delayed. 
 
 Case XXVIII.— (Frangois). Mirant. Had suffered previously 
 from severe pains in the chest and limbs, which compelled him to 
 give up work. Sometime afterward, Avhen the pressure was 4 at- 
 mospheres, he resumed work for a single day — the labor being exces- 
 
50 
 
 sively severe. He suffered no incouveuience apparently, however, 
 and after leaving the caisson, washed his face and hands as usual. 
 A moment after he fell senseless, and in 15 minutes was dead. 
 
 The autopsy was made by a medical commission appointed by the 
 authorities of Valenciennes. The menniges were found to be inject- 
 ed, and the sinuses distended with dark blood. The brain itself was 
 also congested. The spinal canal was not opened. The lungs were 
 somewhat congested, especially at the base, where they were less 
 crepitant than natural, though still floating in water even when cut 
 into small pieces. There was general congestion of the abdominal 
 viscera. (Annales d'Hyg. de Pub. et Med. Legale, 1860.) 
 
 Case XXIX. — The following description of the post-mortem ap- 
 pearances in a case occurring at St. Lou^s, is from Dr. Jaminet's re- 
 port, and may be taken as a type of the morbid anatomy of the Cais- 
 son Disease. 
 
 "Henry Krausman, 27 years ; nativity, Germany ; admitted into 
 the hospital March 22d ; died the 23d. The whole contents of the 
 cranium were found highly congested, with effusion beneath the 
 arachnoid, the vessels of the latter membrane being highly injected. 
 Blood oozed freely from the substance of the brain on section. The 
 spinal cords presented pathological conditions precisely like those of 
 the brain, with the addition of the existence of clots of extravasated 
 blood at different points inside the dura mater. There was alse a 
 congested condition of the thoracic contents, less marked probably in 
 the lungs than in the other organs. The abdominal viscera were 
 very highly congested, with extravasation of blood in the kidneys 
 The mucous membrane of the bladder was healthy, and a small 
 quantity of bloody urine was in the bladder. " 
 
 Case XXX. — John Myers, aged about 40 years, a native of Ger- 
 many, of a stout, heavy build, commenced work in the caisson for 
 the first time on the 22d of April, 1872, the pressure then being 
 about 34 lbs. to the inch. 
 
 He worked during the morning shift of 2^ hom's without in- 
 convenience, and remained about the yard for nearly an hour after 
 coming up. He then complained of not feeling well, and started for 
 his boarding-place, which was but a few rods distant. As he passed 
 through the lower stor}^ of the house, on his Avay to his own room, 
 which was on the second floor, he complained of pain in the abdo- 
 men. While ascending the stairs, and when nearly at the top, he 
 sank down insensible, and was dead before he could be laid upon his 
 bed. 
 
 The autopsy, which took place at the morgue, was made by Dr. 
 Janeway. It showed that the brain, heart, kidneys, and larynx were 
 perfectly normal. The only lesion discovered was in the lungs, which 
 
51 
 
 were congested to a very remarkable degree. The entire extent of 
 both lungs presented an appearance closely resembling that of a 
 highly congested spleen. The spinal canal was not opened ; but 
 nothing was found elsewhere to account for the sudden engorgement 
 of the lungs. 
 
 CHAPTER SEVENTH. 
 
 SUGGESTIONS. 
 
 As it is now demonstrated that the method by compressed au" is ap- 
 plicable to a gi'eat range of engineering operations, and offers many 
 peculiar advantages, it is extremely desu'able that the principal ob- 
 jection to its emplopiient, viz., the discomfort and danger to the 
 workmen, should be reduced to a minimum. To this end I would of- 
 fer the following suggestions, drawn from my own experience and 
 that of European and American observers, to whose writings I have 
 had access. 
 
 It is exceedingly desu'able that the men should be under control to 
 a certain extent during the intervals of work. Excessive use of in- 
 toxicating liquors should be prevented ; regular hours for sleep and 
 for meals insisted upon, and sufficient nutritious, digestible, and 
 properly cooked food should be provided. The men should sleep in 
 comfortable beds and in properly ventilated apartments. 
 
 All this is manif estl}' unattainable if the men live in homes of their 
 own choosiug. If, therefore, any great work by the aid of com- 
 pressed au- is to be undertaken, the preparations for it should include 
 whatever is necessary for housing and feeding the men at a conven- 
 ient place near to the work. For this purix)se temporary barracks 
 may be erected in an enclosure, which the men should not be permit- 
 ted to leave except under proper restrictions. 
 
 The food should be furnished by the employers, be of good quality, 
 embrace a sufficient variety, and be prepared by competent cooks. 
 Sleeping apartments should be provided, allowmg at least 800 cubic 
 feet of air-space to each man. and with facilities for efficient ventila- 
 tion. 
 
 A hospital should be arranged v.'ith a sufficient number of beds, 
 and fitted ^y\th every appliance necessary for treating patients during 
 their entire illness. The hospital to be in charge of a competent 
 steward, under the supervision of a physician, who should attend a 
 portion of each day. 
 
 Of com-se this implies that only single men shall be employed, and 
 that they shall agree at the outset to submit to a quasi military 
 rule. 
 
52 
 
 Where the number of men is considerable, as would l3e the case in 
 any large work, the company could carry out the above suggestions 
 economically to themselves, and after deducting the cost from the 
 pay of the workmen, there would remain to the latter more than 
 they would have left after paying their board in the usual way. At 
 the same time the men would be so much more comfortable than if 
 left to provide for themselves, that they would value the position, 
 and the fear of being discharged would be a sufficient restraint upon 
 them. The tendency, too, w^ould be toward securing at the begin- 
 ning of the work a set of men who would continue to the end. These 
 men commencing when the pressure was slight, would not be affected 
 by its gradual increase, thus avoiding the great danger which attends 
 those who begin work for the first time after the pressure has at- 
 tained a high figure. I am satisfied that it is by attention to this 
 point more than by anything else, that the suffering and danger re- 
 sulting from the use of compressed air may be diminished. (See 
 page 36.) 
 
 New hands should not be allowed to work in the caisson more 
 than one w^atch in each day for the first week, after which half the 
 usual second watch might be added for another week, at the close of 
 which the full time could be entered upon. 
 
 Since much of the work on the pier above, as well as in the caisson 
 below, is unskilled labor, it could readily be so arranged that tliC 
 gangs could work on alternate days in the compressed and in the 
 external air. The advantage of an interval in the caisson work is 
 immediately apparent, the cases of sickness being notably diminished 
 by even a single day's intermission. 
 
 The rules given at p. 15 are important, and their observance 
 should be strenuously insisted upon. 
 
 The men should be selected as far as possible from those who are 
 of a spare and wiry build, and no one should be accepted who has a 
 tendency to corpulency. 
 
 The lock-tenders should be selected with special reference to their 
 trustwortliiness, and, if it is found that they cannot be depended 
 upon, the au--cocks should be so arranged that the aperture can be 
 graduated from time by the engineer in charge, so as to prevent the 
 possibility of a too rapid change of pressure. 
 
 In entering the caisson, at least three minutes should be allowed in 
 the lock for each additional atmosphere of pressure, and at least five 
 minutes in coming out. 
 
 As for the number of hours of work daily, the rule given by Mr. 
 Collingwood will serve as a general guide. " Taking it for granted 
 that 12 hours is the extreme time that a man can labor without detri- 
 ment to health, in an ordinary atmosphere, then with a pressure of 
 
53 
 
 two atmospheres, or 15 lbs. additional pressure, lie can labor about 
 one-half that time ; with three atmospheres, about one-third of that 
 time ; and with four atmospheres about one-fourth of that time. In 
 other words, the time is inversely as the pressure."* 
 
 Whenever, for any cause, a sudden increase of pressure is demand- 
 ed, the watch should be shortened to a corresponding extent. 
 
 The air-locks should be placed at the top rather than at the bottom 
 of the shaft, in order that the stair may be climbed in the compressed 
 air, instead of immediately after leaving the lock, when the system 
 is more or less prostrated by the change taking place in the circula- 
 tion. If, for any reason, it is impracticable to have the air-lock at 
 the top of the shaft, an elevator should be emploj^ed to lift the men 
 to the surface. 
 
 Care should be taken to maintain the air in the caisson at a suffl- . 
 cient degree of purity, as there may be a Avide difference between 
 the amount of air required to supply the necessary mechanical condi- 
 tions for carrying on the work, and the quantity demanded for the 
 health of the workmen. A rough but useful test for the presence of 
 carbonic acid in the air has already been described at p. 14. This is 
 very easily applied, and should be frequently resorted to when there 
 is the least doubt as to the sufficiency of the air supply. A compari- 
 son of the results with those obtained in some fairly ventilated 
 apartment, will give an idea of the amount of impurit}^ in the air of 
 the caisson. The comparison will be aided by allowing the carbonate 
 of lime formed to settle to the bottom of the test tube, where the 
 quantity caif be more readily appreciated. 
 
 ANDEEW H. SMITH. 
 
 * Traus. Am. Society of Civil Engineers, p. 133. 
 
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